Polymorphous Sweat Gland Carcinoma: An Immunohistochemical and Molecular Study

Investigation of the RB1-SOX2 axis constitutes a tool for viral status determination and diagnosis in Merkel cell carcinoma

MCC (Merkel cell carcinoma) is an aggressive neuroendocrine cutaneous neoplasm. Integration of the Merkel cell polyomavirus (MCPyV) is observed in about 80% of the cases, while the remaining 20% are related to UV exposure. Both MCPyV-positive and -negative MCCs-albeit by different mechanisms-are associated with RB1 inactivation leading to overexpression of SOX2, a major contributor to MCC biology. Moreover, although controversial, loss of RB1 expression seems to be restricted to MCPyV-negative cases.The aim of the present study was to assess the performances of RB1 loss and SOX2 expression detected by immunohistochemistry to determine MCPyV status and to diagnose MCC, respectively.Overall, 196 MCC tumors, 233 non-neuroendocrine skin neoplasms and 70 extra-cutaneous neuroendocrine carcinomas (NEC) were included. SOX2 and RB1 expressions were assessed by immunohistochemistry in a tissue micro-array. Diagnostic performances were determined using the likelihood ratio (LHR).RB1 expression loss was evidenced in 27% of the MCC cases, 12% of non-neuroendocrine skin tumors and 63% of extra-cutaneous NEC. Importantly, among MCC cases, RB1 loss was detected in all MCPyV(-) MCCs, while MCPyV( +) cases were consistently RB1-positive (p < 0.001). SOX2 diffuse expression was observed in 92% of the MCC cases and almost never observed in non-neuroendocrine skin epithelial neoplasms (2%, p < 0.0001, LHR +  = 59). Furthermore, SOX2 diffuse staining was more frequently observed in MCCs than in extra-cutaneous NECs (30%, p < 0.001, LHR +  = 3.1).These results confirm RB1 as a robust predictor of MCC viral status and further suggest SOX2 to be a relevant diagnostic marker of MCC.

Microcystic adnexal carcinoma: report of rare cases

Microcystic adnexal carcinoma (MAC) is a rare, locally aggressive malignant neoplasm that derives from cutaneous eccrine/apocrine glands. MAC is classified as an eccrine/apocrine gland tumor and usually occurs in the skin. Here, we characterized and compared two cases of MAC. One is extremely rare in terms of its occurrence in the tongue. The other occurred in the lip, which is common. Histories of disease, diagnosis, and differentials were reviewed by the attending physicians. Hematoxylin and Eosin (HE) slides were evaluated by an experienced pathologist. Immunological markers for malignant eccrine/apocrine gland tumors were used to characterize the tumor’s nature. The examined markers included EMA, CK5/6, CK8/18, CK7, CK20, p63, S-100, Calponin, CD10, MYB, Bcl-2, Her-2, CD34, SMA, p53, CD43, CD117, and Ki-67. Both patients were males, presented with painless lumps in the lower lip and in the tongue, respectively. Both lumps were similar in terms of appearance, being whitish, and infiltrative with irregular borders. Both tumors also had similar histological features with nests of bland keratinocytes, cords, and ductal differentiation filled with Periodic acid–Schiff (PAS)-positive eosinophilic material. In both cases, circular or ovary tumor cells invaded into muscles and nerves. All tumor cells were CK5/6, CK8/18, EMA, and CK7 positive. Particularly, keratinocytes were p63 positive, and paraductal cells were p63, S-100, and SMA positive. Therefore, the rare case of MAC in the tongue appears to derive from the salivary gland.

Malignant Sweat Gland Tumors

Malignant sweat gland neoplasms are a confusing area within dermatopathology, with many entities reported under several designations in the literature. This review describes the key clinical and histopathologic features of select malignant adnexal neoplasms, including porocarcinoma, papillary carcinoma, adenoid cystic carcinoma, cribriform carcinoma, apocrine hidradenocarcinoma, malignant mixed tumor of the skin, syringoid carcinoma, cylindrocarcinoma, spiradenocarcinoma, mucinous carcinoma, polymorphous sweat gland carcinoma, microcystic adnexal carcinoma, secretory carcinoma of the skin, and primary cutaneous signet ring cell carcinoma. For entities with overlapping features, differential diagnoses are discussed.