The natural history of small renal masses

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Abstract
The incidence of renal cell carcinoma is increasing, in part due to the growing use of cross-sectional imaging. Most renal tumors are now incidentally detected as small masses in asymptomatic patients. A minority of small renal masses, presumed to be renal cell carcinoma, grow significantly over time if managed conservatively, but the growth rate of the majority is slow or undetectable. In the absence of other prognostic factors, measurement of tumor growth rate can be helpful for initial conservative management of selected patients with small renal tumors. To date, there have been no reports of progression to metastatic disease occurring during active surveillance, but longer follow-up is needed to confirm this observation. The standard of care for small localized renal neoplasms is partial or radical nephrectomy. At the present time, active surveillance of small renal masses, with delayed therapy for patients whose disease progresses, is an experimental approach that can be considered for the elderly or patients with significant comorbidity. Renal core biopsy and fine-needle aspiration can provide essential information for treatment decision-making and should therefore be considered in the diagnostic work-up of all small renal masses. In future, the identification of prognostic indicators, with the use of new techniques including functional imaging and molecular or genomic characterization of tissue from needle biopsies, are expected to help clinicians differentiate between indolent and potentially aggressive small renal tumors.