Apocrine intraductal carcinoma in situ in nevus sebaceus: two case reports.

Ductal carcinoma in situ (DCIS) in the mammary glands consists of a proliferation of ductal luminal cells with preserved polarity but lacking the marked intercellular cohesion of hyperplastic cells. We report two cases of DCIS arising in the apocrine glandular structures of a nevus sebaceus (NS). The first patient was a 44-year-old woman with a ductal neoplasm composed of multilayered ductal elements with a monomorphous cellularity and a polar orientation of nuclei. The neoplastic cells were positive for Cm5.2 and CK7. The second patient was a 67-year-old woman with phacomatosis pigmentokeratotica. A skin biopsy of an erythematous plaque within her NS showed an epithelioid monomorphous tumor with eosinophilic and slightly granular cytoplasm. Slight nuclear pleomorphism with some hyperchromatic nuclei was seen. The tumor cells were positive for CK7 and gross cystic disease fluid protein-15. Actin showed a preserved layer of myoepithelial cells in both cases. Our cases are noteworthy, as secondary malignancies or multiple tumors arising in NS are rare, and the presence of multiple neoplasms in phacomatosis pigmentokeratotica is even rarer. Moreover, these tumors expand the spectrum of secondary malignant neoplasms arising in NS, as they closely resemble mammary DCIS.