Primary Cutaneous Adenoid Cystic Carcinoma: Report of a Classic Case.

Summary: Adenoid cystic carcinoma (ACC) of the skin is an exceedingly rare entity, typically presenting as a slowly growing nodule. We present a case of primary cutaneous ACC in a middle-aged man who developed a solitary lesion on the right forearm. The tumor was excised, and histopathological evaluation revealed a biphasic neoplasm composed of ductal cells exhibiting tubular duct-like and cribriform patterns, surrounded by myoepithelial cells. The tumor demonstrated grade 1 cytological atypia, with no significant solid patterns observed. Immunohistochemical analysis supported the diagnosis, showing diffuse cytoplasmic CD117 and CK7 expression in ductal cells, along with cytoplasmic smooth muscle actin positivity in myoepithelial cells. There was no evidence of perineural or lymphovascular invasion, and surgical margins were clear. Comprehensive clinical and pathological correlation ruled out tumor presence at other anatomical sites, confirming the diagnosis of primary cutaneous ACC. This case highlights the classic morphological and immunohistochemical features of cutaneous ACC and emphasizes the importance of accurate diagnosis and thorough clinical correlation in such rare presentations.