CA9 as a molecular marker for differential diagnosis of cystic renal tumors.

OBJECTIVE

CA9 is proven to be a powerful marker for clear cell renal cell carcinoma. The studies on CA9 have been limited to solid renal cell carcinomas (RCC). We have conducted a study of CA9 expression in renal cystic tumors. The purpose of the present study was to extend the utility of CA9 for cystic renal tumors.

MATERIALS AND METHODS

Immunohistochemistry and enzyme-linked immunosorbent assay (ELISA) were used to detect CA9 expression in cystic renal tumors. Forty-three cystic renal tumors (22 benign and 21 malignant) were included for the immunohistochemical staining. Thirty-six patients with a cystic renal mass (20 malignant and 16 benign cystic tumors) were studied to measure CA9 level in the fluid by ELISA. Sixteen cysts (9 malignant and 7 benign cysts) were subjected both to immunohistochemistry and CA9 measurement in the fluid.

RESULTS

Using immunohistochemical staining, all the benign cystic renal tumors including the 18 simple cyst and 4 benign multilocular cystic nephromas did not express CA9. All 13 cystic clear cell RCC were scored as strong staining for CA9. For 8 multilocular clear cell RCC, 7 were scored as strong staining for CA9 and the other one was negative. There was a significant difference in positive percentage (P < 0.001) between the 2 groups of malignant and benign cysts. For the 16 benign cysts, the mean concentration of CA9 in the fluid of cyst was 162 ± 133 pg/ml (median: 0 pg/ml; range: 0-2140 pg/ml). For the 20 malignant renal cystic tumors, the mean concentration of CA9 in the fluid of cyst was 2043 ± 62 pg/ml (median: 2,140 pg/ml; range: 1,112-2,140 pg/ml). There was a significant difference in mean concentration of CA9 between the two groups of malignant and benign cysts (P < 0.001). The presence or absence of CA9 expression measured by immunohistochemistry and ELISA test was concordant in 14 out of 16 cases (88%).

CONCLUSIONS

Malignant cystic renal tumors expressed strongly CA9 while the benign renal cysts did not express CA9. CA9 can be detected in the fluid of malignant cystic renal tumors. CA9 is a promising molecular marker to differentiate the malignant cystic renal tumors from the benign cysts.