Quantstudio test

Participants were CYP2D6 and CYP3A4*22 genotyped using the Infiniti Biofilm Microarray (Autogenomics Carlsbad, USA) and the Quantstudio test (ThermoFisher Scientific Waltham, USA). CYP2D6 phenotype was assayed in the laboratory on the genetic variants *2 to *10, *12, *14, *17, *29, and *41; thereafter, patients were classified into four phenotypes based on enzyme function. Consecutively, the CYP2D6 activity score (AS) was calculated according to their allele combination and according to the sum of the AS, participants were assigned to four phenotypes: poor metabolizer (PM; AS = 0), intermediate metabolizer (IM; AS ≥ 0.5 to ≤ 1.0), normal metabolizer (NM; AS ≥ 1.5 to ≤ 2.5), and ultra-rapid metabolizer (UM; AS ≥ 3.0). Additionally, all participants were assigned to a phenotype based on their allele combination, including PM/PM, IM/PM, IM/IM, NM/PM, NM/IM, and NM/NM. All participants were genotyped for CYP3A4*22 for wild type (CC), heterozygous (CT), and homozygous (TT). Activity score calculations and phenotyping were in agreement with the Clinical Pharmacogenetic Implementation Consortium guidelines [30 (link)].

Blood samples for determination of tamoxifen and endoxifen pharmacokinetics were obtained at 13 predefined time points (t = 0 (before tamoxifen intake); and 0.5 h; 1 h; 1.5 h; 2 h; 2.5 h; 3 h; 3.5 h; 4 h; 6 h; 8 h; 10 h and 24 h after tamoxifen intake). Single measurements of plasma concentrations were performed on a validated liquid chromatography with a tandem mass spectrometry method (UP-LC-MS/MS)^{30 (link)}. Using Phoenix WinNonLin version 8.3 the following pharmacokinetic parameters were determined or calculated: area under the plasma concentration time curves (AUC), Cmin and maximum observed plasma concentration (Cmax) of tamoxifen and endoxifen.
CYP2D6 genotyping was performed on germline DNA using the Infiniti test (Autogenomics; Carlsblad, CA, USA) and the Quantstudio test (ThermoFisher Scientific; Waltham, MA, USA). Blood samples were assayed on the follow genetic variants: *2–10, *12, *13, *14, *17, *29, and *41.