Sarcomatoid Eccrine Porocarcinoma in a Patient with Urothelial Carcinoma

Abstract

Introduction/Objective Sarcomatoid porocarcinoma of skin is an exceedingly rare and diagnostically challenging malignancy of the sweat gland. In this report, we describe a rare case of a sarcomatoid eccrine porocarcinoma initially diagnosed to be a squamous cell carcinoma (SCC) in a patient with metastatic urothelial carcinoma (UC). Methods/Case Report Our patient is a 60 year old male with stage IV, poorly differentiated UC status post TURBT with residual tumor, and a 4 x 3 x 1 cm, polypoid, ulcerating skin nodule on his right cheek presumptively diagnosed to be an SCC on biopsy at an outside hospital. Given the concern that this cutaneous lesion may be a metastatic UC with squamous differentiation, the skin nodule was re-biopsied at our hospital. On histology, the lesion consisted of sheets of squamoid, polygonal cells in the dermis with pleomorphic nuclei showing irregular contours, prominent nucleoli, coarse chromatin, and frequent mitoses. The tumor was focally connected to the epidermis, which established it as a primary skin neoplasm and not a metastatic lesion. The tumor cells stained diffusely positive for vimentin, AE1/AE3, CK5/6, HMW CK, CK7, p63, and p16, negative for CK20, GATA-3, BerEP4, and Sox10, and showed high Ki67 proliferation index. Within the tumor sheets were poorly formed, focal ductal elements that stained positive for CAM5.2, EMA, CEA, and CK19, and negative for p63. The tumor showed comedo necrosis, epidermal ulceration, and no keratinization. The tumor was diagnosed to be a porocarcinoma given its positive staining for CK7 and p16, presence of focal ductal elements, and epidermal connection, with sarcomatoid features indicated by strong vimentin expression. Results (if a Case Study enter NA) NA. Conclusion In this report, we described an exceedingly rare, diagnostically challenging case of a sarcomatoid porocarcinoma initially suspected to be a cutaneous SCC or metastatic UC with squamous differentiation. Although the tumor cells morphologically resembled SCC, its positive staining for CK7 and p16, presence of ductal elements, and lack of keratinization, favored a diagnosis of porocarcinoma rather than cutaneous SCC. Its focal connection to the epidermis and lack of GATA-3 expression favored a primary skin neoplasm rather than a metastatic UC. Its sarcomatoid nature was indicated by strong vimentin expression. Sarcomatoid porocarcinoma is diagnostically challenging given its rarity and potential to mimic other cutaneous malignancies such as SCC.