OBJECTIVETo investigate the clinicopathological features and the differential diagnosis of poroma and porocarcinoma.

METHODSHistopathological characteristics and clinical data of 35 cases of poroma and 10 cases of porocarcinoma were analyzed retrospectively.

RESULTSThe average age of 35 patients of poroma was 48 years. The average age of 10 patients of porocarcinoma was 65 years. Both poroma and porocarcinoma occured most frequently on the scalp and face,as well as the extremities. Histologically, cases of poroma were divided into three subtypes, including classic poroma (23 cases), hidroacanthoma simplex (3 cases) and dermal duct tumor (9 cases). Residual foci of benign poroma were found in all cases of porocarcinoma, most of which were classic poroma. The malignant components showed severe dysplasia and/or stromal infiltration.

CONCLUSIONThe diagnosis of poroma and porocarcinoma is mainly based on the microscopic characteristics. An invasive architectural pattern and/or significant cytologic pleomorphism are the most important clues for the diagnosis of porocarcinoma. Neither focal mitotic activity nor the presence of necrosis was the diagnostic feature of porocarcinoma. Malignant transformation can occur in some cases of long existing poroma with recent, rapid tumor enlargement.