Association of polymorphic drug metabolizing enzymes (DME) with outcomes in breast cancer patients treated on the ECOG 2190/Intergroup 0121 (E2190/Int0121) study

Abstract

596 Background: Disparate outcomes of breast cancer patients after adjuvant chemotherapy may be influenced by variation in drug metabolism due to genetic polymorphisms in DME. Cyclophosphamide and thiotepa require activation by cytochrome P450 (CYP) and detoxification by glutathione-S-transferase, two highly polymorphic enzymes. We hypothesized that variants in CYP3A4(*1B), GSTM1 and GSTT1 would impact survival outcomes after adjuvant chemotherapy, with effects potentially modulated by chemotherapy dose. Methods: We performed a retrospective cohort study of patients enrolled on E2190/Int0121, a randomized trial of cyclophosphamide (C), doxorubicin (A), and fluorouracil (F) versus CAF + high dose chemotherapy (HDC) using cyclophosphamide and thiotepa followed by stem cell rescue; disease-free survival (DFS) and overall survival (OS) were equivalent in the clinical trial. PCR-based methods were used to genotype hematologic stem cells. Hazard ratios for genotypes were obtained using Cox regression. Results: Stem cell samples and clinical data from August 1, 1991 through August 1, 2005 were available for 347/540 of patients enrolled; 151 patients on CAF and 196 on CAF + HDC arms, respectively. Median follow-up was 9.8 years. See table . CYP3A4*1B allele carriers had significantly poorer DFS (HR 1.84) in the combined cohort and CAF arm (HR 1.87), but not in the HDC arm; OS was not significant by CYP3A4 genotype. GSTM1 null homozygotes in the combined cohort and HDC arm had significantly better DFS (HR 0.70 and 0.66, respectively) and OS (HR 0.67 and 0.57, respectively), but not in the CAF arm. GSTT1 null homozygotes had significantly worse DFS (HR 2.3) and OS (2.02) in the CAF arm, but not in the HDC arm or combined cohort. Conclusions: In the overall E2190/Int0121 cohort, polymorphisms in activating (CYP3A4*1B) and inactivating (GSTM1) DME significantly impact DFS and OS. The detrimental effect of GSTT1 in the CAF arm appears to be ameliorated by HDC. [Table: see text] No significant financial relationships to disclose.