Clinicopathological characteristics, immunohistochemistry-based surrogate subtypes and survival in male breast cancer
Abstract
Aims: Male breast cancer (MBC) is a rare disease, and treatment approaches are largely extrapolated from female breast cancer. This study aims to evaluate clinicopathological features, immunohistochemistry-based surrogate subtypes, treatment approaches, and survival outcomes in MBC patients from Turkiye, where data on this rare disease remain limited. Methods: Forty-seven MBC patients diagnosed between 2005-2024 were retrospectively analyzed. Demographic characteristics, tumor features, immunohistochemistry-based surrogate subtypes, treatment modalities, and survival data were evaluated. Survival analyses were performed using the Kaplan-Meier method, and group comparisons were conducted using the log-rank test. Exploratory associations with overall survival (OS) were evaluated using univariate Cox regression analysis. Analyses used available cases without imputation. Surrogate subtypes were derived from ER, PR, HER2 and Ki-67; HR-positive/HER2negative tumours without Ki-67 were not assigned to luminal A-like or luminal B-like/HER2-negative categories. Results: The median age was 58.4 years (range 31–90), and the median follow-up was 54.9 months (range 2.8–197.3). Stage II was the most common presentation (59.5%), and stage III–IV disease was present in 28.6%. ER/PR/HER2 data were available for 44 patients. Complete five-category immunohistochemistry-based surrogate subtype classification was possible in 35 patients: luminal A-like 31.4% (11/35), luminal B-like/HER2-negative 42.9% (15/35), luminal B-like/HER2-positive 17.1% (6/35), HER2 positive/non-luminal 5.7% (2/35), and triple-negative 2.9% (1/35). Nine additional HR-positive/HER2-negative tumours could not be divided into the two HER2-negative luminal categories because Ki-67 was unavailable. ER positivity was 93.2%, PR positivity 86.4%, and HER2 positivity 18.2%. OS was evaluable in 46 patients; the median OS was 194.3 months and the median disease-free survival was 155.8 months. In exploratory univariate Cox analysis, older age (per 10-year increase: HR 1.76, 95% CI 1.03–2.98, p=0.037), grade 3 histology (HR 3.35, 95% CI 1.17–9.59, p=0.024) and a high Ki-67 index (≥20% vs