p63 and smooth muscle actin expression in low‐grade spiradenocarcinomas in a case of CYLD cutaneous syndrome

Low‐grade spiradenocarcinoma is a rare skin tumor, with fewer than six reported cases, arising in the context of CYLD cutaneous syndrome (CCS; syn: Brooke‐Spiegler syndrome [BSS]). We report two independent cases of spiradenocarcinoma arising in a 50‐year‐old man with CCS. The tumors grew rapidly, prompting clinical excision. The histologic features in our cases corresponded to the salivary gland type basal cell adenocarcinoma‐like pattern, low grade (BCAC‐LG), that has been previously recognized as a recurrent finding in CCS. We performed genetic testing of the patient and found a novel mutation in CYLD. Recognition of low‐grade spiradenocarcinoma can be difficult for the pathologist as the features can be subtle, especially in those cases where the transition from benign to malignant tumor is gradual. We examined p63 and smooth muscle actin (SMA) expression patterns in BCAC‐LG and compared it with the expression pattern in the precursor spiradenoma. Our report provides information on two rare tumors in the context of CCS and suggests that the pattern of p63 and SMA staining may aid pathological detection of the BCAC‐LG subtype of spiradenocarcinoma.