Immunohistochemical and morphologic evaluation of primary cutaneous apocrine carcinomas and cutaneous metastases from ductal breast carcinoma

The differential diagnosis between a primary cutaneous apocrine carcinoma (CAC) and a cutaneous metastasis from a breast carcinoma can be a very difficult task if it is only made on morphologic bases. Concerning adnexal tumors (in general), there have been many attempts to define an immunohistochemical panel, and while a definition is useful in certain respects, the series presented often times does not include examples of CAC. Other times, CAC seems to behave in an odd way in an immunohistochemical context; they behave differently than other adnexal tumors, and this in turn adds a grade of confusion to the differential diagnosis of a cutaneous metastasis. In the current study, we include seven cases of primary cutaneous apocrine tumors, including one carcinoma in situ, five infiltrating carcinomas, and one adenoma. Additionally, we examine the expression of estrogen receptors (ER), progesterone receptors (PR), and c-erbB-2. We also study myoepithelial markers, such as p63, D2-40, and SMA in them, as well as the pattern of expression of the following cytokeratins: CK7, CK8, CK18, CK19, CK5/6 and 34betaE12. On the other hand, we examine the expression of six immunohistochemical markers (ER, PR, p63, mammaglobin, CK5/6 and D2-40) in 30 cases of cutaneous metastases from breast carcinoma, ductal type. None of our infiltrating primary CAC expressed ER or PR, while the cutaneous metastasis expressed the markers in 90% of the cases. D2-40 was expressed in 60% of the infiltrating CACs, while the metastases were either negative (93.33% of the cases) or positive with luminal reinforcement. Mammaglobin was a very useful marker, expressed by 66.66% of the metastases, and by only one CAC (and in less than 10% of the cells). None of the metastases were positive for p63, while 60% of the CAC expressed the marker. CK 5/6 was also expressed by a high percentage of our CACs (80%), while it was seen in only 6.66% of the metastases. We found SMA as a very useful tool in diagnosing an invasion in CAC. Regarding the expression of c-erbB-2, all of our cases had a value of either 0 or 1.