Immunohistochemical Characterization of the Androgen Receptor in Breast Cancer and Its Relationship with Breast Cancer Subtypes

Background/Objectives: Breast cancer is the most frequent malignant neoplasm in women and presents marked biological heterogeneity. The androgen receptor (AR) has emerged as a biomarker with important prognostic and therapeutic implications, its effect varying according to the molecular subtype. The objective of this study was to analyze AR expression in breast carcinoma samples and its relationship with the different molecular subtypes and clinicopathological variables. Methods: An observational, descriptive, cross-sectional, and prospective study was conducted based on the immunohistochemical analysis of 215 formalin-fixed, paraffin-embedded breast carcinoma samples. AR expression was digitally evaluated as the percentage of positive tumor cells after incubation with an anti-AR monoclonal antibody. Results: A high frequency of AR expression was demonstrated in the cohort, with a median of 53.3%. There were statistically significant differences between molecular subtypes (p < 0.001), detecting greater expression in luminal tumors and markedly low levels in triple-negative breast cancer (TNBC) (median 0.41%). A significant negative correlation was evidenced between AR expression and the Ki-67 proliferation index (ρ = −0.272; p < 0.001), both in the overall sample and in the TNBC subgroup. Conclusions: The androgen receptor is associated with specific molecular subtypes and lower tumor proliferation, suggesting a less aggressive phenotype and supporting its role as a biological biomarker and potential therapeutic target in the management of breast cancer.