Predictive Value of Molecular Subtypes in Premenopausal Women with Hormone Receptor–positive Early Breast Cancer: Results from the ABCSG Trial 5

Purpose: To assess the predictive value of molecular breast cancer subtypes in premenopausal patients with hormone receptor–positive early breast cancer who received adjuvant endocrine treatment or chemotherapy.

Experimental Design: Molecular breast cancer subtypes were centrally assessed on whole tumor sections by IHC in patients of the Austrian Breast and Colorectal Cancer Study Group Trial 5 who had received either 5 years of tamoxifen/3 years of goserelin or six cycles of cyclophosphamide, methotrexate, and fluorouracil (CMF). Luminal A disease was defined as Ki67 <20% and luminal B as Ki67 ≥20%. The luminal B/HER2-positive subtype displayed 3+ HER2-IHC or amplification by ISH. Recurrence-free survival (RFS) and overall survival (OS) were analyzed using Cox models adjusted for clinical and pathologic factors.

Results: 185 (38%), 244 (50%), and 59 (12%) of 488 tumors were classified as luminal A, luminal B/HER2-negative and luminal B/HER2-positive, respectively. Luminal B subtypes were associated with poor outcome. Patients with luminal B tumors had a significantly shorter RFS [adjusted HR for recurrence: 2.22; 95% confidence interval (CI), 1.41–3.49; P = 0.001] and OS (adjusted HR for death: 3.51; 95% CI, 1.80–6.87; P < 0.001). No interaction between molecular subtypes and treatment was observed (test for interaction: P = 0.84 for RFS; P = 0.69 for OS).

Conclusions: Determination of molecular subtypes by IHC is an independent prognostic factor for recurrence and death in premenopausal women with early-stage, hormone receptor–positive breast cancer but is not predictive for outcome of adjuvant treatment with tamoxifen/goserelin or CMF.

See related commentary by Hunter et al., p. 5543