Oral Etoposide and Trastuzumab Use for HER2-Positive Metastatic Breast Cancer: A Retrospective Study from the Institut Curie Hospitals

Background: The TOP2A and ERBB2 genes are co-amplified in about 40% of HER2 positive (HER2+) breast cancers. Oral etoposide (VP16), an inhibitor of topoisomerase-II (encoded by TOP2A), has demonstrated clinical activity in metastatic breast cancer (MBC). The benefit of oral VP16 combined with trastuzumab (VP16-T) in HER2+ MBC has not yet been evaluated. Methods: Patients treated at the Institut Curie Hospitals with VP16-T for HER2+ MBC were retrieved by an in silico search. Progression-free survival (PFS), overall survival (OS), response rate, prolonged PFS (defined as at least 6 months), clinical benefit, and toxicity were assessed. The co-amplification of ERBB2 and TOP2A was assessed by shallow whole genome sequencing on tumor tissue whenever available. Results: Forty-three patients received VP16-T after a median number of six prior treatment lines for HER2+ MBC. Median PFS and OS were 2.9 months (95% CI [2.4–4.7]) and 11.3 months (95% CI [8.3–25.0]), respectively. Three patients had a complete response, while 12/40 (30%) experienced clinical benefit. Only three patients stopped treatment for toxicity. Seven (35%) patients displayed a TOP2A/ERBB2 co-amplification. No statistically significant correlation was found between outcome and TOP2A/ERBB2 co-amplification. Conclusion: Our analysis suggests a favorable efficacy and toxicity profile for VP16-T in patients with heavily pretreated HER2+ MBC.