Endocrine mucin-producing sweat gland carcinoma: twelve new cases suggest that it is a precursor of some invasive mucinous carcinomas.

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is an underrecognized low-grade carcinoma with predilection to the eyelid. Only 4 cases of this entity have been described in the literature. Here, we describe 12 cases of EMPSGC. The lesions were twice as frequent in females than males with an average age of 70 years (range, 48-84 years). Clinically, they presented as a slowly growing cyst or swelling. The most common site of occurrence was the lower eyelid (8 cases). Two lesions occurred on the upper eyelid and 2 on the cheek. Histologically, they were well-circumscribed, typically multinodular tumors with solid or partially cystic nodules, frequently showing areas of papillary architecture. Focal cribriform arrangements were also present. The nodules were formed by uniform small- to medium-sized oval to polygonal epithelial cells with lightly eosinophilic to bluish cytoplasm. The nuclei were bland with diffusely stippled chromatin and inconspicuous nucleoli. Intracytoplasmic and extracellular mucin was usually present. Mitotic activity was present but never brisk. All tumors examined immunohistochemically expressed at least one neuroendocrine marker, synaptophysin or chromogranin. CD57 and neuron specific enolase, secondary markers of neuroendocrine differentiation, were expressed in most cases. All tumors tested expressed estrogen and progesterone receptors, cytokeratin 7, low molecular cytokeratin Cam5.2, and epithelial membrane antigen and were negative for cytokeratin 20 and S-100 protein. Calponin, smooth muscle actin, and p63 immunohistochemical stains did not disclose myoepithelial cells around larger tumor nests in most cases, supporting the notion that EMPSGC is an invasive carcinoma. In 10 cases, cystic areas lined by benign epithelium indistinguishable from eccrine ducts were present. In some foci, the benign ductal epithelium was undermined or replaced by carcinoma in situ with similar cytologic features to the solid or papillary areas of EMPSGC. Myoepithelial cells were preserved in the areas of in situ carcinoma. In 6 cases, EMPSGC was associated with invasive mucinous carcinoma. In situ carcinoma and mucinous carcinoma also expressed neuroendocrine markers. Clinical follow-up showed no recurrences or metastases, consistent with low-grade carcinoma. The series provides histologic evidence for a multistage progression of noninvasive sweat gland neuroendocrine carcinoma to EMPSGC and then to mucinous carcinoma of the eyelid. Although the data from this series support the notion that the prognosis of EMPSGC and mucinous carcinoma is good, longer follow-up is needed for better understanding of their pathogenesis and clinical behavior.