The Probability of Aggressive Versus Indolent Histology Based on Renal Tumor Size: Implications for Surveillance and Treatment.

BACKGROUND: While the probability of malignant versus benign 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 managed with active surveillance.

OBJECTIVE: To characterize the probability of aggressive versus indolent histology based on radiographic tumor size.

DESIGN, SETTING, AND PARTICIPANTS: We evaluated patients who underwent radical or partial nephrectomy at Mayo Clinic for a pT1-2, pNx/0, M0 solid renal tumor between 1990 and 2010. Pathology was reviewed by one genitourinary pathologist. High-grade clear-cell renal cell carcinoma (RCC), high-grade papillary RCC, collecting duct RCC, translocation-associated RCC, hereditary leiomyomatosis RCC, unclassified RCC, and malignant non-RCC tumors were all considered aggressive, as well as any tumors demonstrating coagulative necrosis (except low-grade papillary RCC) or sarcomatoid differentiation. The remaining benign and malignant tumors were considered indolent.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: 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 AND LIMITATIONS: Of the 2650 patients included, there were 1860 patients with indolent tumors (300 benign; 1560 malignant) and 790 with aggressive tumors. The 10-yr CSS was 96% for indolent malignant tumors and 81% for aggressive malignant tumors. The predicted percentages of any malignant histology as well as aggressive histology increased with tumor size. Specifically, 2cm, 3cm, and 4cm tumors have an estimated 84%, 87%, and 88% likelihood of malignancy, respectively, and an 18%, 24%, and 29% likelihood of aggressive histology, respectively. For any given tumor size, men had a greater chance of aggressive histology than women. Potential limitations of this observational surgical cohort include selection bias.

CONCLUSIONS: We present tumor size-based estimates of the probability of aggressive histology for renal masses. This information should be useful for initial patient counseling and management.

PATIENT SUMMARY: Active surveillance is an option for kidney masses, even if they are malignant. Beyond knowing whether the mass is benign or cancer, it is important to know whether or not it is an aggressive tumor. This study presents tumor size-specific and sex-specific estimates of the probability of cancer overall and aggressive cancer among patients with a kidney mass in order to aid with initial decision-making.