Immunohistochemical distinction of renal cell carcinoma from other carcinomas with clear-cell histomorphology: utility of CD10 and CA-125 in addition to PAX-2, PAX-8, RCCma, and adipophilin.

Clear-cell renal cell carcinoma (CC-RCC) is the most common primary kidney malignancy, yet this morphology is not unique to renal primary tumors, as clear-cell variants of numerous nonrenal carcinomas of varying lineages exist. Therefore, because of CC-RCC's ability to metastasize to nearly any anatomic location, ancillary studies such as immunohistochemistry are often needed to establish the diagnosis. Despite CD10 and renal cell carcinoma monoclonal antibody (RCCma) being touted as sensitive and specific markers, some have suggested that more recent stains including PAX-2, PAX-8, or adipophilin (ADP) are more robust markers of CC-RCC. In this study, 26 cases of CC-RCC, and 51 nonrenal carcinomas with clear-cell histomorphology (CCM) were stained with CD10, RCCma, PAX-2, PAX-8, and ADP. CA-125 was also included to help distinguish CC-RCC from Müllerian clear-cell carcinomas, due the known expression of PAX-2 and PAX-8 in both these entities. RCCma highlighted 77% of CC-RCC and 27% of the CCM group, whereas CD10 was positive in 85% and 25%, respectively. ADP highlighted all CC-RCC and 45% of CCMs. PAX-2 was positive in 81% of CC-RCC and 24% of CCM, whereas PAX-8 stained 100% of CC-RCC and 39% of CCM. Müllerian-derived tumors (clear-cell carcinomas of the ovary, vagina, and cervix) were positive with PAX-2 and PAX-8 in 69% and 100% of cases, respectively. No cases of CC-RCC stained with CA-125, whereas 88% of the Müllerian-derived tumors were positive. In summary, although new markers such as PAX-2 and PAX-8 tend to be more sensitive markers of CC-RCC, they lose specificity when Müllerian tumors are included. Inclusion of a classic renal marker such as CD10 or RCCma in the immunohistochemical panel, as well as CA-125 obviates this difficulty.