Tamoxifen metabolism predicts drug concentrations and outcome in premenopausal patients with early breast cancer

Abstract

Tamoxifen is the standard-of-care treatment for estrogen receptor-positive premenopausal breast cancer. We examined tamoxifen metabolism via blood metabolite concentrations and germline variations of CYP3A5, CYP2C9, CYP2C19 and CYP2D6 in 587 premenopausal patients (Asians, Middle Eastern Arabs, Caucasian-UK; median age 39 years) and clinical outcome in 306 patients. N-desmethyltamoxifen (DM-Tam)/(Z)-endoxifen and CYP2D6 phenotype significantly correlated across ethnicities (R(2): 53%, P<10(-77)). CYP2C19 and CYP2C9 correlated with norendoxifen and (Z)-4-hydroxytamoxifen concentrations, respectively (P<0.001). DM-Tam was influenced by body mass index (P<0.001). Improved distant relapse-free survival (DRFS) was associated with decreasing DM-Tam/(Z)-endoxifen (P=0.036) and increasing CYP2D6 activity score (hazard ratio (HR)=0.62; 95% confidence interval (CI), 0.43-0.91; P=0.013). Low (<14 nM) compared with high (>35 nM) endoxifen concentrations were associated with shorter DRFS (univariate P=0.03; multivariate HR=1.94; 95% CI, 1.04-4.14; P=0.064). Our data indicate that endoxifen formation in premenopausal women depends on CYP2D6 irrespective of ethnicity. Low endoxifen concentration/formation and decreased CYP2D6 activity predict shorter DRFS.

Figures

Figure 1

Study flow diagram of premenopausal study. co-med, co-medication; HR, hormone receptor; Leb, Lebanon; POSH, Prospective study of Outcomes in Sporadic versus Hereditary breast cancer; Sing, Singapore; Tam, tamoxifen.

Figure 2

Metabolic profiling for tamoxifen (Tam) and five measured metabolites, N-desmethyltamoxifen (DM-Tam), N,N-didesmethyltamoxifen (DDM-Tam), (Z)-endoxifen, 4-hydroxytamoxifen [(Z)-4-OH-DDM-Tam] and norendoxifen [(Z)-4-OH-DDMT-Tam] in study cohorts from Singapore (Sing, N=164), Lebanon (Leb, N=78) and Prospective study of Outcomes in Sporadic versus Hereditary breast cancer (POSH, N=345). Metabolite concentrations are presented as boxplots with whiskers defined by the 5th and 95th percentiles and extreme values outside the whiskers. The two dashed lines for Tam delineate putative non-compliant (⩽40 nM) and poorly compliant (40–150 nM) patients as defined from Tam plasma concentrations. Patients with Tam concentrations <150 nM were excluded from further analyses.

Figure 3

Steady-state plasma concentrations of endoxifen and metabolic ratio DM-Tam/(Z)-endoxifen in premenopausal breast cancer patients according to genotype-based CYP2D6 activity score: (a) Endoxifen concentrations in Singapore (upper panel, N=160, R2=0.38; P<10−12), Lebanon (middle panel, N=77, R2=0.34; P<10−4) and POSH (lower panel, N=306, R2=0.33; P<10−21) cohorts. (b) Metabolic ratios of DMT/(Z)-endoxifen in Singapore (upper panel, R2=0.46; P<10−17), Lebanon (middle panel, R2=0.55; P<10−9) and POSH (lower panel, R2=0.55; P<10−46) cohorts. (c) Metabolic ratio DM-Tam/(Z)-endoxifen across all cohorts (N=548, R2=0.53; P<10−77). Data are presented as boxplots with whiskers defined by 5th and 95th percentiles and extreme values outside the whiskers. DM-Tam, N-desmethyltamoxifen. **P<10−3; ***P<10−5; ****P<10−10. POSH, Prospective study of Outcomes in Sporadic versus Hereditary breast cancer.

Figure 4

Impact of CYP2C19, CYP2C9 and body mass index on tamoxifen metabolite ratios: (a) Metabolic ratio (MR) DDM-Tam/norendoxifen according to the loss-of-function alleles CYP2C19*2/*3 predicting EM, hetEM (heterozygous *2 or *3) and PM (homozygous *2 or *3). (b) MR tamoxifen/(Z)-4-OH-TAM according to CYP2C9 *2/*3 reduced activity alleles defining hetEM (heterozygous *2 or *3) and PM (homozygous *2 or *3) versus EM with normal activity (absence of *2 or *3). (c) MR tamoxifen/DM-Tam stratified by BMI (⩽30 or >30) in all patients, Caucasians and non-Caucasians. Data are presented as boxplots with whiskers defined by 5th and 95th percentiles and extreme values outside the whiskers. BMI, body mass index; DDM-Tam, DiDesmethyltamoxifen; DM-Tam, Desmethyltamoxifen; EM, extensive metabolizer; hetEM, heterozygous EM; PM, poor metabolizer; (Z)-4-OH-TAM, (Z)-4-hydroxytamoxifen.

Figure 5

Kaplan–Meier analyses for an association between (Z)-endoxifen concentrations, metabolic ratio (MR) Desmethyltamoxifen (DM-Tam)/(Z)-endoxifen or CYP2D6 phenotype score and distant relapse-free survival (DRFS) in the POSH cohort. Kaplan–Meier analyses for DRFS and the three predictor variables classified into groups. (a) Steady-state endoxifen concentrations split into four equally-sized patient groups (<14.1, 14.1–24.7, 24.7–35 and >35 nM), (b) MR DM-Tam/(Z)-endoxifen classified by conditional inference trees into three splits (<31, 31–115 and >115), (c) CYP2D6 phenotypes grouped into EM (plus UM), hetEM and PM. Corresponding Mantel–Cox log-rank tests are stratified for ethnicity. EM, extensive metabolizer; hetEM/IM, heterozygous EM/IM; IM, intermediate metabolizer; PM, poor metabolizer; POSH, Prospective study of Outcomes in Sporadic versus Hereditary breast cancer; UM, ultra rapid metabolizer.