This GSK429286A apocrine signature has been shown to identify unambiguously 13 out of 14 ADCIS and 20 out of 33 IACs in a well characterized set of apocrine carcinomas in which more than 90% of the tumor cells exhibited cytological features typical of apocrine cells. Here we describe two additional markers, brain fatty acid binding protein and hydroxymethylglutaryl -CoA synthase 2, which in combination with markers in the protein signature described previously allowed to identify ADCISs and IACs that failed to be detected in previous studies. Moreover, our results demonstrate that HMGCS2 added to the steroid hormone receptor signature identifies apocrine tumors from other breast cancer subtypes with greater sensitivity as compared to steroid receptor profile alone. We have also presented a detailed immunohistochemistry analysis of a set of proteins corresponding to 10 genes selected from transcriptomic signatures that currently characterize molecular apocrine subtype to evaluate the complementarity of these two approaches. The accurate diagnosis of breast apocrine carcinoma remains controversial, mainly due to the rather subjective histopathological criteria and the lack of sensitive and specific biomarkers, which can reliably categorize this subtype of breast carcinoma. The strategy we have employed to generate protein markers to specifically categorize IAC and potentially be used as targets for therapy, is based on the assumption that these Maprotiline hydrochloride lesions arise from apocrine cells, which in turn are derived from normal breast epithelial luminal cells that have undergone apocrine metaplasia, i.e. transition from breast epithelial cells into an apocrine sweat-gland type of cells. Here we report an analysis of the expression of two novel putative protein biomarkers, FABP7 and HMGCS2, in breast lesions undergoing apocrine differentiation: from benign apocrine metaplasia to invasive apocrine carcinoma. We have found that the lesions with apocrine metaplasia as well as apocrine cysts in breast were highly positive for both HMGCS2 and FABP7 as compared to normal non-apocrine mammary epithelial cells, implying their value as novel biomarkers for breast apocrine differentiation.