Expression of prostate-specific membrane antigen in tumor-associated neovasculature of renal neoplasms.

OBJECTIVES: Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells. Recently, PSMA has been found in the neovasculature in association with other solid malignant tumors, including clear cell renal carcinoma (RCC). We studied the expression of PSMA in different primary renal tumors.
METHODS: A tissue microarray was constructed from 60 normal kidney, 21 clear cell RCC (CCRCC), 20 papillary RCC (PRCC), 16 chromophobe RCC, 19 oncocytoma, 14 transitional cell carcinoma, and 19 angiomyolipoma (AML) specimens. This tissue microarray was then immunostained for a vascular endothelial marker CD34 and PSMA. PSMA expression in CD34-positive tumor-associated neovasculature was scored according to the staining intensity and the percentage of vessels. Only diffuse strong or weak, or focal strong PSMA staining was graded as positive.
RESULTS: PSMA was expressed in the proximal tubules of the normal kidney and in the tumor-associated vasculature in the renal tumors. Positive PSMA staining was detected in 76.2% of CCRCC, 31.2% of chromophobe RCC, 52.6% of oncocytoma, 21.4% of transitional cell carcinoma, and 0% of PRCC and AML specimens. Its expression was greater in CCRCC than PRCC, chromophobe RCC, transitional cell carcinoma, and AML (P <0.001), but was not significantly different from the expression in oncocytoma (P = 0.79). PSMA expression did not correlate with the pathologic stage in CCRCC.
CONCLUSIONS: PSMA is differentially expressed in the tumor-associated neovasculature in different renal tumors. It is most commonly detected in CCRCC and rarely detectable in PRCC and AML. This finding suggests that antibodies against PSMA may potentially be used as a diagnostic marker and therapeutic target for renal neoplasms.