Dissecting the effect of hormone receptor status in patients with HER2-positive early breast cancer: exploratory analysis from the ALTTO (BIG 2-06) randomized clinical trial

Purpose Limited evidence exists on the impact of hormone receptor (HR) status to counsel HER2-positive early breast cancer patients receiving adjuvant anti-HER2 therapy. Methods ALTTO (BIG 2-06) was an international, intergroup, open-label, randomized phase III trial in HER2-positive early breast cancer patients randomized to receive 1 year of trastuzumab and/or lapatinib. HER2, estrogen and progesterone receptors were centrally tested for all patients. We investigated the impact of HR status on prognosis, risk of disease-free survival (DFS) events over time, patterns of first DFS events, and factors associated with risk of DFS events overall, in years 0–5 and 6–8. Results Out of 6273 patients included in this analysis, 3603 (57.4%) had HR-positive tumors. Median follow-up was 6.93 years. Five-year and 8-year DFS were 86% and 80% in patients with HR-positive disease, and 83% and 79% in those with HR-negative tumors, respectively. Mean annual hazards of recurrence in years 0–5 were 3% in patients with HR-positive disease and 4% in those with HR-negative tumors, while in years 6–8 they were 3% and 2%, respectively. Distribution of first DFS event in years 6–8 ( P = 0.005) and type of first distant recurrence ( P