Outcomes of her2-positive Early-Stage Breast Cancer in the Trastuzumab Era: A Population-Based Study of Canadian Patients

Breast cancer is heterogenous, with variable expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Overexpression of HER2 is generally considered a negative prognostic feature, but whether outcomes for HER2-positive early breast cancer remain different from those for other subtypes in the era of trastuzumab-based adjuvant therapy is unknown. Methods: Using a retrospective chart review, we compared overall survival (OS) and relapse-free survival (RFS) in 3 groups of patients with early-stage breast cancer: ER-positive or PR-positive (or both) and HER2-negative [“hormone receptor–positive” (HR+)]; HER2-positive (HER2+); and ER-negative, PR-negative, and HER2-negative [“triple-negative” (TN)]. Results: In the 503 charts analyzed (332 HR+, 94 HER2+, 77 TN), the 5-year OS and RFS were, respectively, 94.2% and 87.2% for HR+ patients, 88.6% and 74.9% for HER2+ patients, and 85.4% and 76.2% for TN patients. On multivariate analysis, the OS for the HER2+ subtype was similar to that for the HR+ subtype (hazard ratio:1.07; 95% confidence interval: 0.31 to 3.67 with HR+ as reference), but OS was significantly worse for TN patients than for HR+ patients (hazard ratio: 4.37; 95% confidence interval: 1.56 to 12.24). In HER2+ patients, the 5-year OS and RFS trended better for patients with ER+ or PR+ disease than for patients with ER-negative and PR-negative disease (5-year OS: 92.1% vs. 86.9%; 5-year RFS: 79.8% vs. 71.4%). Of HER2+ patients, just 80.9% received trastuzumab, including 33.3% of HER2+ patients with sub-centimetre tumours. Conclusions: In the trastuzumab era, patients with HER2+ and HR+ early breast cancer have similar outcomes, while TN patients experience a significantly worse OS than either of the foregoing groups. Outcomes for HER2+ patients may differ by ER and PR status. Trastuzumab was underutilized in this cohort.