Relationship between androgen receptor and androgen receptor-related protein expression in breast cancers focusing on morphologically identified carcinoma with apocrine differentiation

Breast cancer (BC) is classified based on the expression of histopathological markers, namely, estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2). Carcinomas with apocrine differentiation (CAD) are classified based on morphology. Androgen receptor (AR) is highly expressed in CAD; however, no study has comprehensively examined AR-related proteins in CAD. Therefore, we examined the expression of AR-related proteins and AR, compared protein expression patterns between morphologically identified CAD and other BC subtypes, and investigated CAD characteristics. We performed immunohistochemistry for AR and various AR-related proteins in 66 invasive ductal carcinoma (32 ER+/PgR+/HER2-, 8 ER+/PgR+/HER2+, 12 ER-/PgR-/HER2+, and 14 ER-/PgR-/HER2- [triple-negative breast cancer)), 21 invasive lobular carcinoma, and 27 CAD cases. In the CAD group, all cases were AR-positive; some AR-related proteins were highly expressed. Nuclear phosphorylated-mammalian target of rapamycin was highly expressed in CAD cases compared with that in other BC groups, with a 33.3% sensitivity and 97.7% specificity. AR-expressing CAD cases exhibited high expression of other AR-related proteins. Specifically, the combination of AR+, GCDFP15+, and ER - or AR+, FOXA1+, and ER - may be useful for the diagnosis and treatment of AR-positive BC and CAD. These results may assist in androgen-related molecular targeted therapy research.