Metastatic renal cell carcinoma to the bladder: a clinicopathologic and immunohistochemical study.

Although rare, renal cell carcinoma (RCC) can metastasize to the bladder. When this occurs, it might complicate diagnosis. Morphologically, RCC can be confused with transitional cell carcinomas (TCCs), especially those exhibiting clear cell features, and also with other bladder tumors, such as paragangliomas and metastatic melanomas. We report seven cases of RCC metastatic to the bladder that occurred in 6 men and 1 woman who were 35 to 69 years old. The most common presenting symptom was the reappearance of hematuria, which developed from 2 to 131 months (mean, 41.3 mo) after the removal of the primary RCC. In all of the patients, the metastatic RCC involved multiple organs; no case had an isolated metastasis to the bladder. The prognosis was poor, and five patients died of disease between 4 and 24 months (mean, 12.8 mo) after diagnosis of the metastasis to the bladder. The remaining two patients were lost to follow-up. All of the tumors were conventional clear or "granular" cell RCCs, with nuclear grades of 2 or 3. In five patients, metastases were confined to the lamina propria, but in two patients, tumors involved the muscularis propria as well. A comparative immunohistochemical study showed that metastatic RCCs were positive for CAM5.2, vimentin, and Leu-M1, and negative for cytokeratin 20, cytokeratin 7, 34betaE12, carcinoembryonic antigen, S-100 protein, HMB45, and chromogranin. Classic and clear cell TCCs were positive for all of the cytokeratins and carcinoembryonic antigen and negative for vimentin. Paragangliomas were positive for chromogranin and showed scattered positivity for the S-100 protein in the sustentacular cells. Metastatic melanomas were positive for S-100 protein and HMB45. The histologic appearance of RCC, particularly the delicate fibrovascular stroma with abundant sinusoidal vessels, is a feature that can be used to recognize the tumor. When there is difficulty diagnosing metastatic RCC, TCC, or other tumors in the bladder, the immunohistochemical findings can assist in the differential diagnosis.