Characteristics and Outcomes in Cases of US Male Patients with Metastatic Breast Cancer Receiving Abemaciclib in Routine Clinical Practice

INTRODUCTION: Breast cancer in males constitutes approximately 1% of all breast cancer cases globally. Despite extensive treatment experience with abemaciclib in women with metastatic breast cancer (MBC), real-world evidence in male MBC is lacking. METHODS: This analysis was a part of a broader, retrospective study that analyzed electronic medical records and charts of 448 men and women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) MBC who initiated an abemaciclib-containing regimen from January 2017 through September 2019. Data were collected from the Florida Cancer Specialists & Research Institute and the Electronic Medical Office Logistics Health Oncology Warehouse Language™ databases and summarized descriptively. Real-world best response was described: complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD). RESULTS: Data for six male patients with MBC who were treated with abemaciclib in combination with an aromatase inhibitor (AI) or fulvestrant are presented. Four patients were aged ≥ 75 years, and four patients had ≥ 3 metastatic sites, including visceral involvement. Abemaciclib was initiated in/after third-line (≥ 3L) in four patients, and patients had history of treatment with AI (n = 4), chemotherapy (n = 3), and/or prior cyclin-dependent kinase 4 and 6 inhibitors (n = 2) in the metastatic setting. Abemaciclib + fulvestrant was the most common abemaciclib-containing regimen (n = 4). Best response was documented in four patients: 1 each with CR, PR, SD, and PD. CONCLUSION: Prevalence of male MBC in this dataset was consistent with expected prevalence in the broader population. Most male patients received an abemaciclib-containing regimen in ≥ 3L, with anti-cancer activity observed despite heavy metastatic burden and prior treatments in a metastatic setting.