Association of Ki-67 Proliferation Index with Intrinsic Subtypes of Male Breast Cancer in a Ugandan Cohort

Globally, male breast cancer (MBC) is an infrequent disease presentation that carries a poorer outlook relative to its female counterpart; nonetheless, published research on MBC is sparse, particularly within resource-constrained environments. Our goal was to investigate Ki-67 expression and its links to clinicopathological parameters and intrinsic subtypes in a cohort of male breast cancer (BC) patients from a setting with limited resources. A cross-sectional methodology was utilized, drawing upon retrospectively collected information. Data were analyzed for 54 male BC cases diagnosed over an 11-year window from January 2014 to December 2024. The work was undertaken within the Department of Pathology at the Uganda Cancer Institute (UCI) in Kampala, Uganda, spanning February to June 2025. Information was sourced from electronic repositories, patient medical charts, and laboratory requisition forms. To evaluate the relationship between the absolute Ki-67 value (mean) and the clinical/pathological features, as well as BC intrinsic subtypes, a one-way analysis of variance was employed; this was followed by multivariable linear regression modeling to control for potential confounders. The cohort’s average age stood at 56.4 ± 15.1 years, and the youngest individual was 25 years old. Advanced disease (stage III and IV) was present in 68.5% (38/54) of patients. Correspondingly, the ER+, PR+, and HER2− intrinsic subtype was the dominant category, accounting for 68.5% (37/54) of tumors. Following adjustment via multivariable linear regression, solely the intrinsic BC subtypes (95% confidence interval [CI] = 3.397-16.503, P = .032) and PR status (95% CI = 5.693-24.397, P = .042) persisted as significant determinants of Ki-67 expression. Our results reveal elevated expression in MBC tumors that are triple-negative or lack PR expression. This observation suggests that elevated Ki-67 expression in MBC may serve as a marker for categorizing male BC patients by tumor aggressiveness.