Effect of level of hormone-receptor expression on treatment outcomes of "triple-positive" early-stage breast cancer.

Purpose: Breast cancer that overexpresses the human epidermal growth factor receptor-2 (HER2) and both estrogen (ER) and progesterone (PR) receptors is recently recognized as a subtype (triple-positive) with distinctive behavior and response to treatment. In this study, we investigate the treatment outcomes and the beneficial effect of anti-HER2 treatment in relation to level of hormone-receptor (HR) expression.
Methods: Consecutive breast cancer patients with triple-positive disease, diagnosed, treated and followed at our institution between 2006 and 2016 were enrolled. Disease-free survival (DFS) was studied in relation to the level of HR-positivity.
Results: During the study period, a total of 312 were enrolled; median age (range) was 47 (20-83) years. Fifty (16.0%) of the enrolled patients received adjuvant chemotherapy without trastuzumab (cohort A). All remaining patients were treated with both chemotherapy and trastuzumab and were divided into two groups: Cohort B with both ER and PR scores ≥ 50% (n = 130, 41.7%) and Cohort C with ER and/or PR < 50% (n = 132, 42.3%). After a median follow-up of 47 months, 14 (28.0%), 30 (23.1%) and 20 (15.2%) patients in cohorts A, B, and C had an event in a form of local/system relapse or death while disease-free. The estimated 5-year DFS was 56.2%, 75.4%, and 80.8%, respectively, and at 7 year was 56.2%, 67.1%, and 78.0%, respectively (p < 0.001).
Conclusions: HER2-positive tumors are not homogeneous; stronger ER/PR co-expression may weaken the beneficial effect of anti-HER2 therapy. Such findings may have potential implication on modifying anti-HER2 treatment based on the strength of HR expression.