Expression of renal cell carcinoma antigen (RCC) in renal epithelial and nonrenal tumors: diagnostic Implications.

Antibody to renal cell carcinoma (RCC) antigen, a normal human proximal brush border antigen, has recently become commercially available and reported to be highly specific and a relatively sensitive marker for RCC. Of the nonrenal tumors occasional carcinomas have been reported to express RCC, notably breast carcinoma. Using tissue microarrays, we investigated the use of RCC on a large number of renal epithelial neoplasms (RENs) and nonrenal tumors, especially those potentially confused with REN. Three tissue microarrays containing 241 REN samples, 192 samples of a wide variety of neoplasms and 170 adrenal tumor samples, respectively, were stained with RCC monoclonal antibody. RCC expression was scored for staining intensity and percentage expression. Out of 241 REN, 173 were positive for RCC (sensitivity 72%): clear cell 72%, papillary 95%, chromophobe 91%, unclassified 85%, oncocytoma 75%, sarcomatoid 20%, and metastatic RCC 40%. The overall immunostaining intensity was consistently much higher in papillary and clear cell RCC than in other tumors. Seventy-six out of 362 nonrenal tumor samples demonstrated either focal or diffuse expression for RCC (specificity 79%). These included: adrenocortical neoplasms 37/170 (22%), colonic 11/29 (37.5%), breast 9/27 (33%), prostate 5/18 (27.7%), ovary 2/17 (11.7%), melanoma 3/18 (16.6%), lung 3/21 (14.2%), and parathyroid 3/3 (100%). RCC expression was seen equally among adrenal adenoma and carcinoma group. Eight out of 28 (28.5%) normal adrenal cores also stained for RCC. RCC is a relatively useful marker in the differential diagnosis of REN only if used in a panel with other positive and negative markers. RCC does not reliably differentiate REN, especially classic clear cell type, from adrenocortical neoplasms, which are frequently confused due to close anatomic proximity and similar morphology. RCC also does not reliably differentiate subtypes of renal epithelial neoplasms.