We evaluated our experience with renal cortical tumors to determine whether tumor size is associated with malignant histology and/or nuclear grade.

We identified 2,675 patients treated surgically at our institution for renal cell carcinoma or a benign tumor between 1989 and 2007. Histological subtype and tumor size were obtained from our kidney cancer database and logistic regression analysis was performed.

Of the 2,675 tumors 311 (12%) were benign and 2,364 (88%) were renal cell carcinoma. The OR for the association of malignancy with tumor size was 1.16 (95% CI 1.11-1.22, p <0.001), indicating that each 1 cm increase in tumor size was associated with a 16% increase in the odds of malignancy. The incidence of benign tumors decreased from 38% for tumors less than 1 cm to 7% for tumors 7 cm or greater. In patients with clear cell renal cell carcinoma each 1 cm increase in tumor size increased the odds of high grade disease (Fuhrman grade 3-4) compared with low grade disease (Fuhrman grade 1-2) by 25% (OR 1.25, 95% CI 1.21-1.30, p <0.001). In this subset the incidence of high grade lesions increased from 0% for tumors less than 1 cm to 59% for tumors greater than 7 cm.

Our results confirm previous observations suggesting that the risks of malignancy and high grade tumors increase with tumor size. Patients with small renal masses are at low risk for harboring a high grade clear cell malignancy, which may be useful during initial consultation.