The probability of indolent versus aggressive histology based on renal tumor size: Implications for surveillance and treatment

704 Background: While the probability of benign versus malignant histology based on renal tumor size has been described, this alone does not sufficiently inform decision-making in the modern era since indolent malignant tumors can be surveilled. Thus, we sought to characterize the probability of indolent versus aggressive histology based on radiographic tumor size. Methods: We evaluated patients who underwent radical or partial nephrectomy at Mayo Clinic for a pT1-2, pNx/0, M0 solid renal tumor between 1990-2010. Pathology was reviewed by one genitourinary pathologist. Benign tumors, low grade (1-2) clear cell and papillary renal cell carcinoma (RCC), and any chromophobe, clear cell papillary, mucinous tubular and spindle cell, SDH-B deficient, and tubulocystic RCC were considered indolent. All other histologies were considered aggressive, as were any malignancies with necrosis or sarcomatoid differentiation. Cancer-specific survival (CSS) was estimated using the Kaplan Meier method. Logistic regression models were used to estimate the probability of malignant and aggressive histology based on tumor size. Sex-stratified analyses were also performed. Results: Of the 2650 patients included, there were 1773 patients with indolent tumors (303 benign; 1470 malignant) and 877 with aggressive tumors. Ten-year CSS was 96% for indolent malignant tumors and 82% for aggressive tumors. The predicted probabilities of any malignant histology and aggressive malignant histology increased with tumor size (Table; 1-7cm point estimates shown). For example, a 3 cm tumor had an 87% probability of malignancy and a 27% probability of being aggressive. For any given tumor size, men had a greater probability of aggressive histology than women. Conclusions: We present tumor size-based estimates of the probability of aggressive histology for renal masses. This information should be useful for patient counseling and treatment decision-making. [Table: see text]