Abstract

The diagnosis of primary cutaneous adnexal carcinoma can be challenging as many cases may not fit well-defined diagnostic categories. Herein, we present a unique case of a 71-year-old male with primary adnexal carcinoma with squamous, microcystic, and glandular features distinct from known entities with immunohistochemical and molecular profiling. The patient's prior medical history included metastatic pancreatic cancer, and he presented with a left cheek lesion with increasing size over a period of two months. Physical examination revealed a 9mm dome shaped papule with central crusting. Histologic sections of a shave biopsy specimen demonstrated an invasive carcinoma with a nested tubular architecture composed of peripheral squamoid and central microcystic glandular elements. Immunohistochemistry with p40 highlighted peripheral squamoid cells. EMA and CK7 highlighted central microcystic glandular elements. Next-generation sequencing detected mutations in ARID1A, KRAS, MTAP, RNF43, BRAF, CDKN2A, CDKN2B, FAM123B, KDM6A, and TERT promoter. This particular case showed histopathologic features distinct from currently established diagnostic categories. The prominent glandular component and lack of keratin microcysts is inconsistent with a diagnosis of microcystic adnexal carcinoma. There was no superficial appearance of squamous cell carcinoma, excluding squamoid eccrine ductal carcinoma. No mucinous component suggestive of mucoepidermoid carcinoma or adenosquamous carcinoma was noted. The histology was dissimilar from the patient’s pancreatic metastatic carcinoma. This primary adnexal carcinoma, which we are tentatively referring to as squamoglandular microcystic carcinoma, shows molecular findings common to adnexal carcinomas but not specific for known entities. Awareness of the spectrum of findings in this category of neoplasms is key for proper diagnosis.