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 < 0.001) were significantly different between the two groups. Risk factors for DFS events overall, in years 0–5, and 6–8 were different in patients with HR-positive and HR-negative tumors. Conclusions: HER2-positive early breast cancer is characterized by the presence of two diseases with distinct natural history based on HR status requiring the development of different follow-up strategies and future de-escalation and escalation clinical trials.