Well differentiated (grade 1) clear cell renal carcinoma.

We reviewed the experience at this clinic from 1950 to 1980 with cases of grade 1 clear cell renal carcinoma. We wanted to determine whether patients with well differentiated clear cell renal tumors had the favorable clinical course that has been demonstrated for those with well differentiated oncocytic renal tumors. Of the 46 patients identified with pure grade 1 clear cell renal carcinoma two-thirds were discovered incidentally during diagnostic tests for unrelated complaints. These tumors generally were small, with 67 per cent being 6 cm. in diameter or smaller. Of all tumors 83 per cent were pathologic stage 1 (confined within the renal capsule). However, 10 patients have died of metastatic renal carcinoma and 3 are alive with disease. Actuarial survival curves show a significantly poorer prognosis for patients with grade 1 clear cell renal tumors compared to patients with grade 1 oncocytic renal tumors or to an age and sex-matched control group. We conclude that whereas well differentiated oncocytic renal tumors behave like benign renal tumors, well differentiated clear cell renal tumors can behave like aggressively malignant renal carcinomas and should be treated as such.