Diagnosing primary and metastatic renal cell carcinoma - The use of the monoclonal antibody 'renal cell carcinoma marker'

The diagnosis of primary or metastatic renal cell carcinoma (RCC) can be di fficult, especially in small biopsies, because of the wide variety of histo logic appearances and clinical presentations that RCC can assume. An immuno marker specific for RCC is currently not available. We tested the relevant diagnostic use of the Renal Cell Carcinoma Marker (RCC Ma), a monoclonal an tibody, against a normal human proximal tubular brush border antigen. immun ostaining using RCC Ma and the avidin-biotin-peroxidase complex technique w as performed on archival tissues from primary and metastatic tumors of rena l or nonrenal origin. A total of 122 of 153 primary RCCs (79.7%) were posit ive (clear cell (84%), papillary (96%), chromophobe (45%), sarcomatoid (25% , and collecting duct (0%)], with greater than or equal to 10% of tumor cel ls stained in 93% of cases. None of the 64 primary renal tumors other than RCC, including 15 oncocytomas, was positive. Fifteen of 146 (10.2%) nonrena l primary tumors were positive (5 of 17 breast tumors, 8 of 8 parathyroid a denomas, and 2 of 7 embryonal carcinomas). Forty-two of 63 (67%) metastatic RCCs were positive with greater than or equal to 10% of cells being staine d in 83% of them. Two of 108 (2%) metastases from tumors other than RCCs we re positive, both of which were metastatic breast carcinomas; however, only 10% (2 of 19) of metastatic breast carcinomas were positive, RCC Ma is an excellent marker for primary RCC, which should facilitate its diagnosis in a small biopsy. Although RCC Ma remains highly specific (98%) for metastati c RCC, a negative result may not rule out metastatic RCC because of a rathe r low sensitivity and a focal staining pattern in some of the positive case s. RCC Ma may also facilitate the differential diagnosis between oncocytoma and other types of RCC when they are composed mostly of eosinophilic cells .