UBC Faculty Research and Publications

Prognostic and predictive investigation of PAM50 intrinsic subtypes in the NCIC CTG MA.21 phase III chemotherapy trial Liu, Shuzhen; Chapman, Judy-Anne W.; Burnell, Margot J.; Levine, Mark N.; Pritchard, Kathleen I.; Whelan, Timothy J.; Rugo, Hope S.; Albain, Kathy S.; Perez, Edith A.; Virk, Shakeel; Barry, Garrett; Gao, Dongxia; O’Brien, Patti; Shepherd, Lois E.; Nielsen, Torsten; Gelmon, Karen A.

Abstract

Purpose: PAM50-defined breast cancer intrinsic subtypes and risk-of-relapse (ROR) scores are prognostic and predictive of endocrine therapy, and some chemotherapy. We investigated the prognostic and predictive effect of PAM50 classifications by chemotherapy type. Methods: NCIC CTG MA.21 randomized 2104 patients to doxorubicin, cyclophosphamide and paclitaxel (AC/T); dose-intense cyclophosphamide, epirubicin and flurouracil (CEF); or dose-dense, dose-intense epirubicin, cyclophosphamide and paclitaxel (EC/T). Patients were ≤60 years, with node-positive or high-risk node-negative disease, with median 8-year follow-up. Intrinsic subtypes and ROR were determined from RNA extracted from formalin-fixed paraffinembedded sections by the NanoString PAM50 test. Univariate effects on relapse-free survival (RFS) were assessed with stratified log-rank test; multivariate analyses utilized stratified Cox regression. Results: Among 1094 cases completing PAM50 intrinsic subtyping, 27% were classified as luminal A, 23% luminal B, 18% HER2E, and 32% basal-like. CEF and EC/T were superior to AC/T (p=0.01). Higher continuous ROR was multivariately associated with worse RFS (p=0.03), although categorical ROR was neither prognostic nor predictive. Intrinsic subtypes had a significant multivariate prognostic effect on RFS (p=0.002). Compared with luminal A, hazard ratios were: luminal B=1.48 (95% CI= 0.92-2.37); HER2E=2.68 (95% CI=1.60-4.48); basallike=1.97 (95% CI=1.10-3.53). Intrinsic subtypes were not predictive of treatment benefit (AC/T vs EC/T+CEF); however, subgroup analysis indicated subtypes (non-luminal vs. luminal) were predictive of taxane benefit (EC/T vs. CEF; p=0.05). Conclusion: Both NanoString PAM50 subtypes and continuous ROR had significant prognostic effects on RFS for breast cancer patients treated with CEF, EC/T and AC/T. Non-luminal tumors differentially responded to EC/T (with taxane) over CEF.

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