Eccrine or apocrine poroma? Six poromas with divergent adnexal differentiation

We describe six cases of benign eccrine poroma-like neoplasms with divergent adnexal differentiation. Four cases exhibited sebaceous differentiation in the form of individual or clustered sebocytes with or without sebaceous ducts. One case showed both sebaceous and hair follicle differentiation, and one case showed sebaceous and possible apocrine secretory differentiation. Clinically, most were skin-colored, red, or purple papules or nodules. One patient had a preoperative diagnosis of Bowen's disease, with an erythematous plaque. None recurred following biopsy. Previous reports of similar lesions have suggested a possible role for human papilloma virus (HPV) in their pathogenesis; however, immunohistochemical staining for HPV structural antigens was negative in all six of these cases. Similarities to previously reported cases of eccrine poroma-like neoplasms with sebaceous differentiation are discussed. Given the evidence of sebaceous and follicular differentiation seen in this study and the common embryologic origin of follicular, sebaceous, and apocrine structures, it follows that at least some benign neoplastic proliferations with histopathologic features of "eccrine" poroma could be of apocrine origin.