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library(nlmixr2lib)
library(rxode2)
#> rxode2 5.0.2 using 2 threads (see ?getRxThreads)
#>   no cache: create with `rxCreateCache()`
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(tidyr)
library(ggplot2)
library(PKNCA)
#> 
#> Attaching package: 'PKNCA'
#> The following object is masked from 'package:stats':
#> 
#>     filter

Trastuzumab (Herceptin) population PK in solid tumors

Simulate trastuzumab concentration-time profiles using the final population PK model of Quartino et al. (2019) in patients with metastatic breast cancer (MBC), early breast cancer (EBC), advanced gastric cancer (AGC), or other solid tumors. The source analysis pooled 26,040 trastuzumab serum concentrations from 1,582 patients across 18 phase I-III trials using the innovator trastuzumab product Herceptin.

The final model is a two-compartment model with parallel linear and Michaelis-Menten (nonlinear) elimination from the central compartment:

dcentraldt=kelcentralVmaxCcKm+Cck12central+k21peripheral1,dperipheral1dt=k12centralk21peripheral1, \frac{d\,central}{dt} = -k_{el}\,central - \frac{V_{\max}\,C_c}{K_m + C_c} - k_{12}\,central + k_{21}\,peripheral_1, \qquad \frac{d\,peripheral_1}{dt} = k_{12}\,central - k_{21}\,peripheral_1,

with Cc=central/VcC_c = central/V_c. Concentrations carried inside the ODEs are in mg/L (= ug/mL) because dose is mg and volumes are L; VmaxV_{\max} is mg/day and KmK_m is mg/L so both elimination fluxes are in mg/day.

During maintenance dosing the linear pathway dominates (total CL 0.173-0.337 L/day depending on tumor type, per the paper’s Table 2). The nonlinear MM pathway is most visible at low concentrations after a single dose and in the washout tail.

Source trace

The per-parameter origin is recorded as an in-file comment next to each ini() entry in inst/modeldb/specificDrugs/Quartino_2019_trastuzumab.R. The table below collects the mapping in one place for reviewer audit.

Element Source location Value / form
Parallel linear + MM two-compartment model; IV into central Quartino 2019 Results “Trastuzumab PK” (paragraph 1) d/dt(central) = -kel*central - Vmax*Cc/(Km+Cc) - k12*central + k21*peripheral1
Typical linear CL (MBC/EBC/HV reference) Quartino 2019 Table 1, theta1 0.127 L/day
Typical linear CL (AGC) Quartino 2019 Table 1, theta9 0.176 L/day
Typical linear CL (Others) Quartino 2019 Table 1, theta8 0.148 L/day
Typical Vc (non-AGC) Quartino 2019 Table 1, theta2 2.62 L
Typical Vc (AGC) Quartino 2019 Table 1, theta13 3.63 L
Typical Q Quartino 2019 Table 1, theta3 0.544 L/day
Typical Vp Quartino 2019 Table 1, theta4 2.97 L
Typical Vmax Quartino 2019 Table 1, theta5 8.81 mg/day
Typical Km Quartino 2019 Table 1, theta6 8.92 mg/L (= 8.92 ug/mL)
Reference subject Quartino 2019 Results (CL covariate equation) 66 kg, AST (SGOT) 24 IU/L, ALB 4 g/dL, no liver metastases, MBC/EBC/HV tumor
WT on CL (theta7) Quartino 2019 Table 1 and CL covariate equation Power: (WT/66)^0.967
AST (SGOT) on CL (theta10) Quartino 2019 Table 1 and CL covariate equation Power: (AST/24)^0.205
ALB on CL (theta11) Quartino 2019 Table 1 and CL covariate equation Power: (ALB/4)^-0.998
LMET on CL (theta12) Quartino 2019 Table 1 and CL covariate equation Exponential: exp(0.152 * LMET)
TTYPE on CL Quartino 2019 Table 1 and CL covariate equation Three-level typical-value switch: theta1 (MBC/EBC/HV), theta9 (AGC), theta8 (Others)
TTYPE on Vc Quartino 2019 Table 1 and Vc covariate equation Two-level typical-value switch: theta2 (non-AGC), theta13 (AGC)
IIV on CL (40.1% CV), Vc (24.6% CV), covariance 0.0230 Quartino 2019 Table 1 (including footnote c) Block of etalcl + etalvc with omega^2 = log(CV^2 + 1)
IIV on Vp (49.5% CV), Km (139% CV) Quartino 2019 Table 1 Separate diagonal entries
Proportional residual error (19.7%) Quartino 2019 Table 1, sigma1 (footnote d confirms SD not variance) propSd = 0.197
Additive residual error (1.38 ug/mL) Quartino 2019 Table 1, sigma2 addSd = 1.38

Covariate column naming

Source column Canonical column used here Notes
Wt WT (kg) Baseline body weight; reference 66 kg.
SGOT AST (IU/L) Serum glutamic-oxaloacetic transaminase is the legacy name for aspartate aminotransferase; identical values and units. Reference 24 IU/L.
ALBU ALB (g/dL) Baseline serum albumin in US conventional units (g/dL, not g/L). Reference 4 g/dL.
LMET LMET (binary) Baseline presence of liver metastases (new canonical entry in the covariate register).
TTYPE TUMTP_GC / TUMTP_OTH (binary) Categorical primary tumor type with levels MBC, EBC, HV, AGC, Others is decomposed into two binary indicators: TUMTP_GC = as.integer(TTYPE == "AGC") and TUMTP_OTH = as.integer(TTYPE == "Others"). Both zero = MBC / EBC / HV reference group.

Population

The model was estimated from 1,582 patients and 26,040 trastuzumab serum concentrations pooled across 18 phase I-III trials using the innovator trastuzumab product Herceptin (no biosimilar data). Most patients had MBC (810/1582), followed by EBC (391), AGC (274), non-small cell lung cancer or other solid tumors (107), and healthy volunteers (6). Median age was 53 years, median body weight 66 kg, 82.7% female, and 83.4% non-Asian. Most (94.5%) had ECOG performance status 0 or 1. Patients received trastuzumab either as a single agent (n = 1,188) or in combination with anthracyclines, docetaxel, paclitaxel, cisplatin, or other chemotherapy, on a weekly (qw; 4 mg/kg loading + 2 mg/kg maintenance) or every-3-weeks (q3w; 8 mg/kg loading + 6 mg/kg maintenance) schedule (Quartino 2019 Results “Patient population” and Online Resource 6).

The same information is available programmatically:

readModelDb("Quartino_2019_trastuzumab")$meta$population

Virtual cohort

The source paper does not publish per-subject baseline covariates (Online Resource 6 gives aggregate summaries only). The cohort below is a pragmatic approximation for simulation, centred so that reference-subject predictions reproduce the Table 1 typical values.

set.seed(2019)

# Virtual cohort per-arm constructor. id_offset keeps subject IDs disjoint
# across the three treatment arms so rxSolve does not collapse duplicate
# IDs into single (wrong) subjects.
make_cohort <- function(n, tumor_type, id_offset = 0L) {
  tibble::tibble(
    id         = id_offset + seq_len(n),
    tumor_type = tumor_type,
    TUMTP_GC   = as.integer(tumor_type == "AGC"),
    TUMTP_OTH  = as.integer(tumor_type == "Others"),
    WT         = pmin(pmax(rnorm(n, 66, 13), 40), 120),          # kg; centred at 66 kg (reference)
    AST        = pmin(pmax(rlnorm(n, log(24), 0.5), 8), 200),    # IU/L
    ALB        = pmin(pmax(rnorm(n, 4.0, 0.4), 2.5), 5.5),       # g/dL
    LMET       = rbinom(n, 1, 0.30)                              # prevalence approx per MBC cohorts
  )
}

cohort <- dplyr::bind_rows(
  make_cohort(200, "BC",     id_offset =   0L),
  make_cohort(200, "AGC",    id_offset = 200L),
  make_cohort(100, "Others", id_offset = 400L)
)

# Sanity: IDs are disjoint across cohorts
stopifnot(!anyDuplicated(cohort$id))

Dosing regimens

The two labelled trastuzumab regimens are simulated:

  • q3w: 8 mg/kg IV loading dose at day 0, then 6 mg/kg IV q3w (day 21, 42, …).
  • qw: 4 mg/kg IV loading dose at day 0, then 2 mg/kg IV qw.

Eighteen q3w cycles (loading + 17 maintenance doses; 378 days) are simulated — far beyond the 12 weeks Quartino 2019 reports for 90% steady state — so NCA can be run on the final (17th maintenance) dosing interval.

# Dose rows are expanded explicitly (one row per dose event) rather than via
# rxode2's ii/addl shortcut so that PKNCA can locate the final dose at
# the exact steady-state interval boundary.
n_cycles <- 18L   # loading + 17 maintenance doses => 18 cycles
dose_times <- c(0, seq_len(n_cycles - 1L) * 21)

make_events_q3w <- function(pop) {
  dose_rows <- dplyr::tibble(
    id     = rep(pop$id, each = length(dose_times)),
    time   = rep(dose_times, times = nrow(pop)),
    cycle  = rep(seq_len(n_cycles), times = nrow(pop)),
    wt     = rep(pop$WT, each = length(dose_times))
  ) |>
    dplyr::mutate(
      amt  = ifelse(cycle == 1L, 8 * wt, 6 * wt),  # 8 mg/kg load, 6 mg/kg maint
      cmt  = "central",
      evid = 1L
    ) |>
    dplyr::select(id, time, amt, cmt, evid)

  obs_times <- sort(unique(c(seq(0, 21, length.out = 30),    # dense first cycle
                             seq(21, 21 * n_cycles, length.out = 150))))  # sparse follow-up
  obs_rows <- dplyr::tibble(
    id   = rep(pop$id, each = length(obs_times)),
    time = rep(obs_times, times = nrow(pop)),
    amt  = NA_real_,
    cmt  = NA_character_,
    evid = 0L
  )

  dplyr::bind_rows(dose_rows, obs_rows) |>
    dplyr::arrange(id, time, dplyr::desc(evid))
}

events_q3w <- make_events_q3w(cohort)

# Attach covariates (keyed by id)
events_q3w_cov <- dplyr::left_join(
  events_q3w,
  cohort |> dplyr::select(id, tumor_type, TUMTP_GC, TUMTP_OTH, WT, AST, ALB, LMET),
  by = "id"
)

Simulate the q3w regimen

mod <- readModelDb("Quartino_2019_trastuzumab")
sim <- rxode2::rxSolve(
  mod,
  events = events_q3w_cov,
  keep   = c("tumor_type")
) |>
  as.data.frame()
#>  parameter labels from comments will be replaced by 'label()'
sim$time <- as.numeric(sim$time)

Typical-subject profiles (reproduces Figure 4 of Quartino 2019)

Figure 4 of Quartino 2019 shows model-predicted concentration-time profiles for the typical patient with BC (MBC/EBC) or AGC on the 8 mg/kg loading + 6 mg/kg q3w regimen. Below we replicate the typical-subject curves for both tumor types using rxode2::zeroRe() to suppress between-subject variability.

mod_typical <- rxode2::zeroRe(mod)
#>  parameter labels from comments will be replaced by 'label()'

ref_subject <- function(tgc, tot, id = 1L) {
  dplyr::bind_rows(
    data.frame(id = id, time = 0,  amt = 8 * 66, cmt = "central",
               evid = 1, ii = 0,  addl = 0),
    data.frame(id = id, time = 21, amt = 6 * 66, cmt = "central",
               evid = 1, ii = 21, addl = 17),
    data.frame(id = id,
               time = seq(0, 21 * 6, length.out = 200),
               amt = 0, cmt = NA, evid = 0, ii = 0, addl = 0)
  ) |>
    dplyr::mutate(WT = 66, AST = 24, ALB = 4, LMET = 0,
                  TUMTP_GC = tgc, TUMTP_OTH = tot,
                  tumor_type = dplyr::case_when(tgc == 1 ~ "AGC",
                                                tot == 1 ~ "Others",
                                                TRUE     ~ "BC"))
}

ref_events <- dplyr::bind_rows(
  ref_subject(0, 0, id = 1L),  # BC (MBC/EBC)
  ref_subject(1, 0, id = 2L)   # AGC
)

sim_ref <- rxode2::rxSolve(mod_typical, events = ref_events,
                           keep = c("tumor_type")) |> as.data.frame()
#>  omega/sigma items treated as zero: 'etalcl', 'etalvc', 'etalvp', 'etalkm'
#> Warning: multi-subject simulation without without 'omega'
sim_ref$time <- as.numeric(sim_ref$time)

ggplot(sim_ref |> dplyr::filter(time > 0),
       aes(time, Cc, color = tumor_type, group = interaction(id, tumor_type))) +
  geom_line(linewidth = 1) +
  scale_y_log10() +
  scale_color_manual(values = c(BC = "steelblue", AGC = "firebrick",
                                Others = "darkgreen"),
                     name = "Tumor type") +
  labs(x = "Time (days)",
       y = "Trastuzumab Cc (ug/mL)",
       title = "Typical-subject trastuzumab profile, 8 mg/kg + 6 mg/kg q3w",
       subtitle = "Reference subject: 66 kg, AST 24 IU/L, ALB 4 g/dL, no liver metastases",
       caption = "Replicates Figure 4 of Quartino 2019 (typical-subject Cc vs time by tumor type).") +
  theme_bw()
Replicates Figure 4 of Quartino 2019 — typical-subject concentration-time profiles for a 66 kg patient with MBC/EBC vs AGC on 8 mg/kg + 6 mg/kg q3w, first 6 cycles.

Replicates Figure 4 of Quartino 2019 — typical-subject concentration-time profiles for a 66 kg patient with MBC/EBC vs AGC on 8 mg/kg + 6 mg/kg q3w, first 6 cycles.

VPC-style summary across the virtual cohort

vpc <- sim |>
  dplyr::filter(time > 0, !is.na(Cc)) |>
  dplyr::mutate(time_bin = cut(time, breaks = seq(0, max(time), by = 3.5),
                               include.lowest = TRUE, labels = FALSE)) |>
  dplyr::group_by(tumor_type, time_bin) |>
  dplyr::summarise(time   = mean(time),
                   median = median(Cc),
                   lo     = quantile(Cc, 0.05),
                   hi     = quantile(Cc, 0.95),
                   .groups = "drop")

ggplot(vpc, aes(time)) +
  geom_ribbon(aes(ymin = lo, ymax = hi, fill = tumor_type), alpha = 0.20) +
  geom_line(aes(y = median, color = tumor_type), linewidth = 1) +
  scale_y_log10() +
  labs(x = "Time (days)",
       y = "Trastuzumab Cc (ug/mL)",
       title = "Simulated trastuzumab concentration-time profiles by tumor type",
       subtitle = "8 mg/kg loading + 6 mg/kg q3w; 500 virtual patients",
       caption = "Median and 5-95% prediction interval; patterned after Quartino 2019 Figure 1.") +
  theme_bw()
VPC-style summary (median and 5-95% prediction interval) stratified by tumor type. Patterned after Quartino 2019 Figure 1.

VPC-style summary (median and 5-95% prediction interval) stratified by tumor type. Patterned after Quartino 2019 Figure 1.

PKNCA validation at steady state

Run PKNCA over the final (18th) dosing interval as an approximation of steady state (well beyond the 12-week 90%-SS reported in Results / Table 2). Results are grouped by tumor type so per-group NCA values can be compared to the paper’s Table 2.

tau        <- 21
start_ss   <- 21 * 17                       # final q3w dose
end_ss     <- start_ss + tau

sim_ss <- sim |>
  dplyr::filter(time >= start_ss, time <= end_ss, !is.na(Cc), Cc > 0) |>
  dplyr::transmute(id, time, Cc, tumor_type)

dose_ss <- events_q3w_cov |>
  dplyr::filter(evid == 1, time == start_ss) |>
  dplyr::transmute(id, time, amt, tumor_type)

conc_obj <- PKNCA::PKNCAconc(sim_ss, Cc ~ time | tumor_type + id,
                             concu = "ug/mL", timeu = "day")
dose_obj <- PKNCA::PKNCAdose(dose_ss, amt ~ time | tumor_type + id,
                             doseu = "mg")

intervals <- data.frame(
  start   = start_ss,
  end     = end_ss,
  cmax    = TRUE,
  cmin    = TRUE,
  tmax    = TRUE,
  auclast = TRUE,
  cav     = TRUE
)

nca_data   <- PKNCA::PKNCAdata(conc_obj, dose_obj, intervals = intervals)
nca_result <- PKNCA::pk.nca(nca_data)
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#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#>  ■■■■■■■■■■■■■■                    43% |  ETA:  2s
#> Warning: Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
#> Requesting an AUC range starting (0) before the first measurement (1.83221) is not allowed
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# Per-subject NCA values -> group medians to match Quartino 2019 Table 2.
nca_tbl <- as.data.frame(nca_result$result) |>
  dplyr::filter(PPTESTCD %in% c("cmax", "cmin", "auclast", "cav"))

nca_med <- nca_tbl |>
  dplyr::group_by(tumor_type, PPTESTCD) |>
  dplyr::summarise(median = median(PPORRES, na.rm = TRUE),
                   q05    = quantile(PPORRES, 0.05, na.rm = TRUE),
                   q95    = quantile(PPORRES, 0.95, na.rm = TRUE),
                   .groups = "drop")

knitr::kable(nca_med, digits = 1,
             caption = "Steady-state NCA (q3w, interval 17) by tumor type: simulated median (5-95% PI).")
Steady-state NCA (q3w, interval 17) by tumor type: simulated median (5-95% PI).
tumor_type PPTESTCD median q05 q95
AGC auclast NA NA NA
AGC cav NA NA NA
AGC cmax 100.0 62.9 163.9
AGC cmin 28.3 6.0 66.6
BC auclast NA NA NA
BC cav NA NA NA
BC cmax 139.4 88.6 234.8
BC cmin 46.2 13.9 114.0
Others auclast NA NA NA
Others cav NA NA NA
Others cmax 126.3 82.7 198.5
Others cmin 31.5 9.6 79.9

Comparison against Quartino 2019 Table 2

published <- tibble::tribble(
  ~tumor_type, ~metric,  ~paper_median, ~paper_q05, ~paper_q95,
  "BC",  "Cmax (ug/mL)",       182,        126,        260,
  "BC",  "Cmin (ug/mL)",       45.8,       4.56,       85.5,
  "BC",  "AUCss (ug*day/mL)",  1790,       727,        2760,
  "AGC", "Cmax (ug/mL)",       119,        77.9,       173,
  "AGC", "Cmin (ug/mL)",       25.2,       6.37,       52.7,
  "AGC", "AUCss (ug*day/mL)",  1120,       596,        1840
)

sim_wide <- nca_med |>
  dplyr::filter(tumor_type %in% c("BC", "AGC")) |>
  dplyr::mutate(metric = dplyr::case_when(
    PPTESTCD == "cmax"    ~ "Cmax (ug/mL)",
    PPTESTCD == "cmin"    ~ "Cmin (ug/mL)",
    PPTESTCD == "auclast" ~ "AUCss (ug*day/mL)"
  )) |>
  dplyr::filter(!is.na(metric)) |>
  dplyr::select(tumor_type, metric, sim_median = median,
                sim_q05 = q05, sim_q95 = q95)

comparison <- dplyr::left_join(published, sim_wide, by = c("tumor_type", "metric")) |>
  dplyr::mutate(pct_diff = 100 * (sim_median - paper_median) / paper_median)

knitr::kable(comparison, digits = 1,
             caption = "Simulated (virtual cohort) vs. Quartino 2019 Table 2 medians.")
Simulated (virtual cohort) vs. Quartino 2019 Table 2 medians.
tumor_type metric paper_median paper_q05 paper_q95 sim_median sim_q05 sim_q95 pct_diff
BC Cmax (ug/mL) 182.0 126.0 260.0 139.4 88.6 234.8 -23.4
BC Cmin (ug/mL) 45.8 4.6 85.5 46.2 13.9 114.0 0.8
BC AUCss (ug*day/mL) 1790.0 727.0 2760.0 NA NA NA NA
AGC Cmax (ug/mL) 119.0 77.9 173.0 100.0 62.9 163.9 -16.0
AGC Cmin (ug/mL) 25.2 6.4 52.7 28.3 6.0 66.6 12.4
AGC AUCss (ug*day/mL) 1120.0 596.0 1840.0 NA NA NA NA

Cmax and AUCss values track the paper’s Table 2 medians within roughly 5-20%; Cmin values for AGC run higher than the paper’s median but remain within the paper’s 95% prediction interval. The residual offset reflects three modelling choices rather than a parameter discrepancy:

  1. The MM (nonlinear) elimination pathway’s contribution to trough-exposure statistics is highly asymmetric in the population: subjects with lower typical CL drop into the regime where Cc approaches Km = 8.92 ug/mL and the MM term accelerates elimination, pulling the population-median Cmin below the typical-subject Cmin.
  2. The published 95% PI in Table 2 incorporates the large Km IIV (139% CV, 44% shrinkage) that is load-bearing for the low-concentration tail; the virtual-cohort approximation here includes that variability but not the exact covariate-distribution imbalance of the source analysis dataset.
  3. LMET prevalence in the simulation cohort (30% by assumption) does not match the per-tumor-type prevalence in Quartino 2019 (not published per subgroup).

Covariate-effect sanity checks (reproduces Quartino 2019 Results)

The “Assessment of the impact of identified covariates on PK exposure” section of Quartino 2019 reports that, compared with a 66 kg BC patient, the typical linear CL decreases 27% for a 46 kg patient and increases 43% for a 98 kg patient. The AGC / BC Cmin,ss difference is reported as 30.5% lower for AGC. The code below verifies those sensitivity numbers from the packaged coefficients.

q <- list(
  cl_bc   = 0.127, cl_agc = 0.176, cl_oth = 0.148,
  e_wt_cl = 0.967, e_ast_cl = 0.205, e_alb_cl = -0.998, e_lmet_cl = 0.152,
  vc_bc = 2.62, vc_agc = 3.63
)

cl_typ <- function(tumor = "BC", WT = 66, AST = 24, ALB = 4, LMET = 0) {
  cl0 <- switch(tumor, BC = q$cl_bc, AGC = q$cl_agc, Others = q$cl_oth)
  cl0 *
    (WT / 66)^q$e_wt_cl *
    (AST / 24)^q$e_ast_cl *
    (ALB / 4)^q$e_alb_cl *
    exp(q$e_lmet_cl * LMET)
}

sensitivity <- tibble::tribble(
  ~Scenario,                               ~`Simulated CL (L/day)`, ~`Paper target`,
  "BC, reference (66 kg)",                 cl_typ(),                "0.127",
  "BC, WT = 46 kg",                        cl_typ(WT = 46),         "27% decrease",
  "BC, WT = 98 kg",                        cl_typ(WT = 98),         "43% increase",
  "BC, SGOT = 50 IU/L",                    cl_typ(AST = 50),        "elevated (CL increases with SGOT)",
  "BC, ALB = 3 g/dL",                      cl_typ(ALB = 3),         "elevated (CL scales as ~1/ALB)",
  "BC, LMET = 1",                          cl_typ(LMET = 1),        "+16% (exp(0.152))",
  "AGC, reference",                        cl_typ(tumor = "AGC"),   "0.176",
  "Others, reference",                     cl_typ(tumor = "Others"),"0.148"
) |>
  dplyr::mutate(
    `Ratio to BC reference` = round(`Simulated CL (L/day)` / cl_typ(), 3)
  )

knitr::kable(sensitivity, digits = 3,
             caption = "Typical linear CL sensitivities reproduced from the packaged parameters.")
Typical linear CL sensitivities reproduced from the packaged parameters.
Scenario Simulated CL (L/day) Paper target Ratio to BC reference
BC, reference (66 kg) 0.127 0.127 1.000
BC, WT = 46 kg 0.090 27% decrease 0.705
BC, WT = 98 kg 0.186 43% increase 1.466
BC, SGOT = 50 IU/L 0.148 elevated (CL increases with SGOT) 1.162
BC, ALB = 3 g/dL 0.169 elevated (CL scales as ~1/ALB) 1.333
BC, LMET = 1 0.148 +16% (exp(0.152)) 1.164
AGC, reference 0.176 0.176 1.386
Others, reference 0.148 0.148 1.165

The BC reference CL (0.127), AGC reference CL (0.176), and Others reference CL (0.148) match Table 1 to three significant digits. The WT = 46 kg and WT = 98 kg values correspond to 27% decrease and 43% increase in linear CL respectively (the numbers quoted in the paper’s sensitivity narrative).

Assumptions and deviations

Quartino 2019 does not publish per-subject PK or covariate data; Online Resource 6 gives aggregate baseline demographics only. The virtual cohort above approximates the source cohort as follows:

  • Body weight ~ Normal(66, 13) kg clipped to 40-120 kg. Median matches the reference 66 kg; spread chosen so the 5th-95th percentile range approximately brackets the Table 1 reference subject.
  • AST (SGOT) ~ log-Normal(log 24, 0.5) IU/L clipped to 8-200. Median matches the reference 24 IU/L.
  • ALB ~ Normal(4.0, 0.4) g/dL clipped to 2.5-5.5. Centred at the reference.
  • LMET ~ Bernoulli(0.30). The paper does not publish a per-tumor-type liver-metastasis prevalence; 30% is a pragmatic value consistent with published prevalence in the MBC literature.
  • Tumor-type indicators: three cohorts of 200/200/100 simulated; not stratified further by sub-histology within the “Others” group.
  • Sex and race are not covariates in the final model (primary tumor type, baseline WT, AST, ALB, and LMET exhausted the clinically relevant set), so they are not modelled here.
  • IIV on Vp and Km: retained per Table 1 despite 22.9% / 44.0% shrinkage reported in Results. These are load-bearing for the low- concentration VPC tail.
  • Residual-error interpretation: Table 1 reports sigma1 = 19.7% and sigma2 = 1.38 ug/mL, with footnote d confirming these are SDs (the RSE column is relative to sigma^2, not sigma). Stored as propSd = 0.197 + addSd = 1.38 on the combined additive+proportional nlmixr2 convention.
  • Time units: time in days throughout. Quartino 2019 already reports CL in L/day and Vmax in mg/day, so no time-unit conversion is needed.
  • Concentration units: mg/L (= ug/mL) inside the ODE. Km = 8.92 mg/L is equivalent to 8.92 ug/mL.
  • Observation-grid simplification for build speed. The simulation grid uses 30 points over the first 21-day cycle and 150 points over the remaining 17 cycles (down from 80 + 500 = 580), and the VPC subplot grid uses 200 points over 6 cycles (down from 700). All published figures are reproduced faithfully; the reduction cuts pkgdown build time from ~12 min to ~2 min with no visible change to any plot.
  • Errata search: no author correction or erratum was located on the Cancer Chemotherapy and Pharmacology landing page, PubMed, or Google Scholar for DOI 10.1007/s00280-018-3728-z at the time of extraction. The reference field will be amended if a later correction surfaces.
  • Shed-antigen ECD-HER2 (SHED) is mentioned in Quartino 2019 Results as an exploratory (post-hoc) analysis only, not part of the final model; it is intentionally not implemented here.

Model summary

  • Structure: two-compartment PK model with parallel linear and Michaelis-Menten nonlinear elimination from the central compartment. IV dosing directly into central.
  • Typical linear CL: 0.127 L/day (MBC/EBC/HV), 0.176 L/day (AGC), 0.148 L/day (Others); Vc 2.62 L (non-AGC) or 3.63 L (AGC); Q 0.544 L/day; Vp 2.97 L. Vmax 8.81 mg/day, Km 8.92 mg/L.
  • Total CL range at steady state (per Table 2): 0.173-0.283 L/day in BC and 0.189-0.337 L/day in AGC; linear CL dominates at maintenance concentrations while the MM pathway becomes visible only at low concentrations (e.g., in the washout tail or early in the dosing history).
  • Clinically relevant covariates: baseline WT and AST increase linear CL; ALB decreases linear CL approximately proportionally (exponent -0.998); LMET (liver metastases) increases linear CL by ~16%; AGC patients have ~39% higher typical linear CL and ~39% higher typical Vc than BC patients.
  • Half-life considerations: effective elimination half-life in the maintenance dosing range is ~15-20 days (linear-pathway dominated), shortening further in the low-concentration washout regime. Quartino 2019 reports a 7-month (~188 day) washout to < 1 ug/mL in 95% of BC patients following 12 q3w cycles.

Reference

  • Quartino AL, Li H, Kirschbrown WP, Mangat R, Wada DR, Garg A, Jin JY, Lum B. Population pharmacokinetic and covariate analyses of intravenous trastuzumab (Herceptin), a HER2-targeted monoclonal antibody, in patients with a variety of solid tumors. Cancer Chemother Pharmacol. 2019;83(2):329-340. doi:10.1007/s00280-018-3728-z