Nakamura H, Kukita Y, Kunimasa K, et al. - Researchers assessed α-methylacyl-CoA racemase (AMACR), also known as P504S, as a possible marker of carcinoma with apocrine differentiation (an androgen receptor-positive subset of triple-negative breast carcinomas). They analyzed 212 breast carcinomas: 39 carcinomas with apocrine differentiation, 28 ductal carcinomas in situ with apocrine morphology (ADCIS), and 145 non-apocrine breast carcinomas. In carcinomas with apocrine differentiation and in ADCIS, AMACR was found expressed in 38 out of 39 (97.4%) and in 27 out of 28 (96.4%), respectively, consistent with the expression of gross cystic disease fluid protein-15 (GCDFP-15). Findings showed the likely utility of AMACR expression as a tool to distinguish between carcinoma with apocrine differentiation and non-apocrine carcinomas. Results indicated greater sensitivity of AMACR, compared with that of GCDFP-15, as a carcinoma with apocrine differentiation marker.