Clear cell papillary cystadenoma of the epididymis and mesosalpinx: immunohistochemical differentiation from metastatic clear cell renal cell carcinoma.

Clear cell papillary cystadenoma is a rare epithelial tumor of the epididymis, which may present as an isolated lesion or as a component of von Hippel-Lindau disease (VHLD). Recently, tumors have also been described in the female genital tract with similar histology. Recognition of clear cell papillary cystadenoma is critical because of its association with VHLD and its potential diagnostic confusion with metastatic renal cell carcinoma because of a shared architecture and clear cells. In this study, we report on the immunohistochemical differentiation of 5 clear cell papillary cystadenomas, 3 of the epididymis and 2 of the mesosalpinx, from metastatic renal cell carcinoma. In 2 cases, there was a history of renal cell carcinoma in the setting of VHLD; and in 1 of these cases, an epididymal papillary cystadenoma was initially considered to be metastatic renal cell carcinoma. Immunohistochemically, tumor cells were moderately intensely positive for cytokeratin AE1/AE3 and epithelial membrane antigen, strongly positive for CK7 and negative for CK20 and RCC. Four of 5 cases were negative for CD10. This staining profile contrasts with that reported for clear cell renal cell carcinomas, which are typically negative for CK7 and immunoreactive for renal cell carcinoma (RCC) and CD10. Our findings indicate that, in cases where there is uncertainty about the histologic diagnosis of clear cell papillary cystadenoma, the above immunohistochemical panel helps to rule out metastatic renal cell carcinoma.