[A case of primary mucinous carcinoma with endocrine differentiation of the skin].

Primary mucinous carcinoma of the skin (MCS) is a rare skin appendage tumor and only a few cases of MCS with endocrine differentiation have been reported. Here we report an additional case of primary pure MCS with endocrine differentiation arising in the face. Histopathologically, the tumor was located in the dermis and subcutis, and nests of slight atypical epithelial cells were floating in the mucinous pools. This tumor did not accompany carcinoma in situ or invasive non-mucinous carcinoma and was difficult to differentiate from metastatic mucinous carcinoma of the skin. There was no tumor in the other organs and synaptophysin and chromogranin A were sporadically shown immunohistochemically in the tumor cells; a diagnosis of primary pure MCS with endocrine differentiation was made. MCS resembles mammary mucinous carcinoma not only in morphological appearance but also in immunohistochemical phenotypes, such as positive immunoreactivity to gross cystic disease protein fluid-15, MUC2, MUC6, estrogen receptor and progesterone receptor. It is presumed that MCS is derived from the apocrine gland, which is closely related to the mammary gland. Although endocrine differentiation is not uncommon in pure mucinous carcinoma of the breast, there have been only a few reports published on endocrine differentiation in MCS. To clarify the difference and/or similarity between mucinous carcinoma of the breast and MCS, immunohistochemical and cytogenetic analyses of additional cases of MCS are required.