PURPOSE: We examined the relationship between tumor size and malignancy among solid renal tumors, and the relationship between tumor size and RCC subtype within tumors with renal cell carcinoma (RCC). MATERIALS AND METHODS: We identified 2,770 adult patients who underwent radical nephrectomy or nephron sparing surgery for sporadic unilateral nonmetastatic solid renal tumors between 1970 and 2000. All pathology specimens were reviewed by a urological pathologist for diagnosis, and in RCC tumors, for histological subtype and nuclear grade. RESULTS: There were 376 benign (12.8%) and 2,559 (87.2%) malignant tumors. The percentage of benign tumors decreased from 46.3% for those less than 1 cm to 6.3% for those 7 cm or greater. Among RCC tumors the percentage that were clear cell increased from 25.6% for those less than 1 cm to 83.0% for tumors 7 cm or greater, while the percentage that were papillary decreased from 74.4% for those less than 1 cm to 10.0% for tumors 7 cm or greater. No RCC tumors less than 1 cm were chromophobe compared to 7.0% of tumors 7 cm or greater. The percentage of malignant tumors that were high grade RCC increased from 2.3% for those less than 1 cm to 57.7% for RCC tumors 7 cm or greater. Only 1% of all tumors less than 1 cm and 9.2% of all tumors less than 2 cm were high grade malignancies. CONCLUSIONS: As tumor size increased there was a significant increase in the odds of having a malignant compared to a benign tumor, clear cell compared to papillary RCC and high grade compared to low grade malignancy.
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