Immunohistochemistry for the detection of renal cell carcinoma in effusion cytology

Abstract

Renal cell carcinoma (RCC) is known for its unpredictable behavior. RCC rarely involves serosal surfaces and, when present, can be difficult to distinguish from mesothelial cells in cytologic preparations. Immunohistochemical stains are frequently used with effusion cytology; however, RCCs express traditional glandular antigens less frequently than other adenocarcinomas. We investigated the utility of typical immunohistochemical stains for identifying effusion involvement by RCC, along with more specific RCC markers. The cytology databases from two academic institutions were searched for all effusions involved by RCC with retrievable cell-block material. A four-marker immunohistochemical panel we generally use for distinguishing adenocarcinoma from mesothelial proliferations was then applied (calretinin, WT1, MOC31, and B72.3). In addition, each case was stained for RCC antigen, CD10, and PAX2. Eleven cases of RCC involving serous effusions were identified: six conventional clear-cell RCCs, three papillary RCCs, and two RCCs, not otherwise specified. Neoplastic cells were positive for MOC-31 in 3 of 11 cases, RCC antigen in 5 of 11 cases, and CD10 in 10 of 11 cases. RCC cells were negative for B-72.3, WT1, and calretinin in all cases. Background mesothelial cells showed high-background cytoplasmic staining for PAX-2; all RCC tumor cells were negative or equivocal. A conventional panel used for the diagnosis of adenocarcinoma in fluids will fail to detect most cases of metastatic RCC, particularly clear-cell RCC. Additional antibodies, such as those to CD10 and RCC, may be helpful to identify these tumors. PAX2 shows high background in mesothelial cells, which makes interpretation of nuclear staining difficult.