Oral etoposide and trastuzumab in HER2-positive metastatic breast cancer: a retrospective study at 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). However, the clinical benefit of oral VP16 combined with trastuzumab (VP16-T) in HER2+ MBC has not been evaluated.Methods: Patients treated at Institut Curie Hospitals with VP16-T for HER2+ MBC were retrieved by an in-silico search. Trained medical oncologists retrospectively assessed progression-free survival (PFS), overall survival (OS), response rate, prolonged PFS (defined as a duration of at least 6 months), 6 months clinical benefit rate and toxicity. 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%) had a clinical benefit. Only 3 patients stopped treatment for toxicity. Median PFS in the population with and without TOP2A/ERBB2 co-amplification was respectively 4.7 months (95% CI [2.3-NA]) and 2.9 months (95% CI [1.2-NA]; p=0.36).Conclusion: Our analysis suggests a favorable efficacy and toxicity profile for VP16-T in patients with heavily pretreated HER2+ MBC.