First-Line Efficacy of Anti-HER2 Treatments in Previously Treated HER2-Positive Metastatic Breast Cancer Patients: A Retrospective Observational Study Investigating the Efficacy of Re-Exposure to Anti-HER2 Therapy for HER2-Positive Metastatic Breast Cancer Patients in Comparison with Naive Patients

Background: Most patients with HER2-positive metastatic breast cancer (MBC) receive first-line treatment with anti-HER2 agents and have already received anti-HER2 therapy as adjuvant or neoadjuvant therapy in the local setting of their disease presentation. Despite that, they constitute only a minority among clinical trials, and their response to reintroduction to anti-HER2 treatments is inconclusive based upon conflicting studies. We aimed to examine if previous exposure influences the clinical outcome of patients treated with anti-HER2 treatments compared to patients who were naive to anti-HER2 agents. Methods: We conducted a retrospective observational study of HER2-positive MBC patients who were treated with trastuzumab and pertuzumab from 2014 to 2018. We collected and analyzed data including patients' demographic characteristic as well as extracted data of previous treatment regimens and the efficiency of the anti-HER2 therapy measured by response rate (RR), time to tumor progression (TTP), and overall survival (OS). Results: Eighty patients met the inclusion criteria, 26 (32.5%) of them were previously exposed to anti-HER2 treatments and 54 (67.5%) were not previously exposed to anti-HER2 therapy. No significant differences were detected in RR after 3 months of treatment (p = 0.684). TTP was significantly better among patients with no previous exposure in comparison with patients with previous exposure to anti-HER2 therapy (21 vs. 14 months, p = 0.044) and we noted a trend in better OS (p = 0.056). Conclusion: Our analysis suggests that previous exposure to anti-HER2 agents might influence the clinical outcome of first-line treatment in metastatic HER2 patients. These findings justify further exploration of the benefit of reintroduction of anti-HER2 treatment enabling the optimal treatment for patients with previous anti-HER2 therapy exposure.