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

Although rare, renal cell carcinoma (RCC) can metastasize to the bladder. W hen this occurs, it might complicate diagnosis. Morphologically, RCC can be confused with transitional cell carcinomas (TCCs), especially those exhibi ting clear cell features, and also with other bladder tumors, such as parag angliomas and metastatic melanomas. We report seven cases of RCC metastatic to the bladder that occurred in 6 men and I 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 t he primary RCC. In all of the patients, the metastatic RCC involved multipl e 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 tw o patients were lost to follow-up. All of the tumors were conventional clea r or "granular" cell RCCs, nifh nuclear grades of 2 or 3. In five patients, metastases were confined to the lamina propria, but in two patients, tumor s involved the muscularis propria as well. A comparative immunohistochemica l study showed that metastatic RCCs were positive for CAM5.2, vimentin, and Leu-M1, and negative for cytokeratin 20, cytokeratin 7, 34 beta E12, carci noembryonic antigen, S-100 protein, HMB45, and chromogranin. Classic and cl ear cell TCCs were positive for all of the cytokeratins and carcinoembryoni c antigen and negative for vimentin. Paragangliomas were positive for chrom ogranin and showed scattered positivity for the S-100 protein in the susten tacular cells. Metastatic melanomas were positive for S-100 protein and HMB 45. The histologic appearance of RCC, particularly the delicate fibrovascul ar stroma with abundant sinusoidal vessels, is a feature that can be used t o recognize the tumor. When there is difficulty diagnosing metastatic RCC, TCC, or other tumors in the bladder, the immunohistochemical findings can a ssist in the differential diagnosis.