Real-World Evidence of Long-Term Disease Control in HER2-Positive Metastatic Breast Cancer Patients Treated with a First-Line Combination of Trastuzumab and/or Pertuzumab Plus Chemotherapy.

Background and Method: The overexpression of the human epidermal growth factor receptor 2 (HER2) in breast cancer is correlated with accelerated tumor progression and an unfavorable clinical outcome. Since the introduction of trastuzumab in 2002, the treatment of HER2-positive breast cancer has been revolutionized, leading to significant improvements in survival. This retrospective, multicenter study aimed to describe the characteristics of patients with HER2-positive metastatic breast cancer (MBC) who maintained disease control for a minimum of three years after first-line therapy with trastuzumab and/or pertuzumab combined with chemotherapy. Results: Among 280 eligible patients, 48 (17.5%) were classified as long-term responders. The study population primarily consisted of women with a median age of 56.7 years at diagnosis; de novo metastatic presentation was observed in approximately 70% of cases. An objective response rate of nearly 90% was observed, with a median duration of response of 5.8 years. Median progression-free survival was 11.0 years [95% CI: 6.6-not reached], and median overall survival was not reached [95% CI: 10.9-not reached]. Furthermore, about 15% of patients were able to discontinue systemic therapy without immediate disease progression. Discussion and Conclusions: These findings indicate the potential of achieving prolonged disease control in a subset of patients with HER2-positive MBC, raising questions about therapeutic intensification and potential treatment discontinuation strategies. This study underscores the need for future research to identify predictive factors of durable response and assess the feasibility of adaptive treatment strategies, including planned treatment discontinuation.