Pigmented Eccrine Porocarcinoma

Kim, Seung Myun; Lee, Jee Bum; Lee, Seung Chul; Won, Young Ho; Yun, Sook Jung; Kim, Seong Jin

Abstract

Eccrine porocarcinoma is a rare cutaneous neoplasm arising from the eccrine sweat duct. It may arise de novo or evolve from a pre-existing poroma or hidroacanthoma simplex. The pigmented variant of porocarcinoma is very rare, and its heavy pigmentation can lead to misdiagnosis of seborrheic keratosis or melanoma. An 82-year-old male patient presented with a painful, brown-to-black colored plaque measuring 4x4.5 cm with a central pedunculated nodule that measured 2.5x2 cm on his right posterior thigh. A small, pigmented papule had developed 10 years prior and had gradually increased in size. Histopathologic examination of the nodule revealed lobulated tumor islands composed of atypical basaloid cells in the periphery, eosinophilic squamous cells in the center, and pigmented dendritic cells scattered throughout nests of the tumor. Carcinoembryonic antigen and epithelial membrane antigen were expressed in the tumor cells and the dendritic cells stained positive for S-100 and HMB45. Histopathologic findings from the plaque showed many pigmented nests embedded within the epidermis that were composed of small, polygonal, pigmented basaloid cells. Pigmented eccrine porocarcinoma arising from pigmented hidroacanthoma simplex was diagnosed clinically and histopathologically. The tumor was completely excised. We report a case of pigmented porocarcinoma, which should be included among clinically important differential diagnoses apart from melanoma.