Metastatic male breast cancer: What do we know about treatment efficacy and survival? a multicenter retrospective study.

e13100 Background: Male breast cancer is a rare malignancy, representing less than 1% of all breast cancer cases worldwide. While treatment outcomes in breast cancer have improved substantially, male patients remain underrepresented in prospective trials, resulting in limited high-quality evidence to guide clinical decision-making. In routine practice, men are often diagnosed at an early stage and respond well to standard therapies. In the metastatic setting, however, the disease behaves as a chronic condition requiring long-term systemic treatment. Methods: A retrospective multicenter study across eight Polish cancer centers included 244 men diagnosed with breast cancer between 2010 and 2025. Clinical data on patient characteristics, tumor features, treatment modalities, and survival outcome were analyzed. Survival outcomes analyses were performed using Kaplan-Meier method and median overall survival (OS), progression-free survival (PFS) and survival rates were reported. Results: In the palliative cohort (79 patients), luminal breast cancer represented the largest biological subgroup (46%), followed by HER2-positive disease (28%). HER2-low tumors were particularly rare, occurring in 22 patients (28%), a rate lower than typically reported in unselected breast cancer populations. By contrast, triple-negative disease was extremely rare (n = 1). Median progression-free survival (PFS) was 16.5 months in the first-line setting and 12.6 months in the second line. Despite the predominance of hormone receptor–positive disease, CDK4/6 inhibitors were administered to only five patients. In first-line therapy, median PFS reached 20 months for luminal tumors and 16.5 months for HER2-positive disease. Bone, lung, and liver were the predominant sites of metastatic disease. Overall survival in the palliative cohort remained relatively prolonged, with a median OS of 47.5 months and a 5-year OS rate of 42.2%. Conclusions: Despite substantial progress in breast cancer treatment overall, the management of male breast cancer remains a significant clinical challenge. The current evidence base is still limited. Larger, well-designed studies are therefore required to better characterize this rare disease and to develop more effective, evidence-based therapeutic strategies for male patients.