A Case of Eccrine Porocarcinoma: Usefulness of Immunostain for S-100 Protein in the Diagnoses of Recurrent and Metastatic Dedifferentiated Lesions
A 78-year-old Japanese woman visited our hospital, complaining about the left inguinal skin tumor, increasing in size (). Since biopsy revealed the lesion is malignant, the dermal tumor was excised, and local lymphadenectomy was also performed. Neoplastic cells proliferated in lobular downwards growth, and connected to the epidermis (). The neoplastic cells have atypical oval nucleus, and mitotic figures were found. A small number of lumens were observed in the nests. Melanin granules were not found. Immunostain for carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) is positive at the rims of the lumens (). Majority of the lesion was immunoreactive for AE1/AE3. On immunohistochemistry for S-100 protein, scattered stained dendritic cells were found (). On that for HMB-45 and Melan-A, scattered positive cells were found partially. Some tumor cells appeared to be periodic acid schiff (PAS) stain positive, and PAS-positive substance was digested by diastase. There was no nodal metastasis. According to these facts, the diagnosis of EPC was confirmed. After fourteen months, a tumor occurred in the same location. Epithelioid cells diffusely proliferated in the subcutaneous tissues (). The histology looked like epithelioid melanoma. Immunostain for CEA and EMA was negative, but immunoreactivity for AE1/AE3 was diffusely observed. Scattered S-100 protein positive cells were found (). But, immunoreactivity for Melan-A and HMB-45 disappeared. The cells contain no PAS-positive glycogen. Since the tumor location is same with that of the primary lesion, and the stainings for S-100 protein and AE1/AE3 between the two are similar, the lesion was diagnosed as recurrent EPC with dedifferentiation. Three months later, metastasis to the lungs was found. Biopsied specimens showed similar histologic findings of the secondary inguinal lesion, and the diagnosis of dedifferentiated metastatic EPC was made. Immunoreactivity for AE1/AE3 was diffusely observed, and scattered immunoreactive cells for S-100 protein were also maintained. Nevertheless, immunostains for EMA, HMB-45, and Melan-A were all negative. Two months later, the patient died for aggravation of general condition.