Apocrine carcinoma as triple-negative breast cancer: novel definition of apocrine-type carcinoma as estrogen/progesterone receptor-negative and androgen receptor-positive invasive ductal carcinoma.

OBJECTIVE Apocrine carcinoma, a subtype of invasive ductal carcinoma of the breast, expresses androgen receptor (AR), but often lacks estrogen receptor (ER) and progesterone receptor (PgR). In the present study, the author immunohistochemically defined apocrine-type carcinoma as ER-/PgR-/AR+ invasive ductal carcinoma and analyzed the significance of apocrine-type carcinoma as triple-negative breast cancer. METHODS Four hundred and forty breast cancers from 429 cases were immunostained for estrogen receptor, progesterone receptor, androgen receptor, human epidermal growth factor receptor type 2 (HER2), p53, Ki-67 and epidermal growth factor receptor. The lesions included 58 in situ malignancies (including 13 apocrine-type lesions) and 325 invasive ductal carcinomas (including 44 apocrine type). RESULTS Of 91 estrogen receptor-negative invasive ductal carcinomas, 44 (48%) belonged to apocrine-type carcinoma, and overexpression of human epidermal growth factor receptor type 2 and p53 was observed in 23 (52%) and 33 (75%), respectively. Histologically, 22 (50%) were categorized as classical apocrine carcinoma. Among 281 non-apocrine invasive ductal carcinomas, 30 (11%) were quadruple-negative (ER-/PgR-/AR-/HER2-) and 17 (6%) were hormone receptor-negative and human epidermal growth factor receptor type 2-overexpressed. Invasive ductal carcinomas in the triple-negative breast cancer category (n= 51) were divided into triple-negative, androgen receptor-positive (apocrine, n= 21) and quadruple-negative (non-apocrine, n= 30). p53 overexpression was more often seen in the apocrine-type triple-negative breast cancer (18/21 = 86%) than in the non-apocrine type (14/30 = 46%) (P< 0.05). Ki-67 labeling was significantly higher in the non-apocrine type (58%) than in the apocrine type (37%) (P< 0.01). Epidermal growth factor receptor is consistently expressed in triple-negative breast cancers (16/16 = 100% in apocrine and 18/20 = 90% in non-apocrine). CONCLUSIONS Androgen receptor should be added to immunohistochemical panels, since apocrine-type invasive ductal carcinoma, resembling basal-like phenotypes, may show clinical behaviors different from the basal-like triple-negative breast cancer.