Natural History of Small Renal Masses

Objective: To review the natural history and growth kinetics of small renal masses (SRMs). Data Sources: The literature concerning natural history and growth kinetics of SRMs was collected from PubMed published from 1990 to 2014. Study Selection: We included all the relevant articles on the active surveillance (AS) or delayed treatment for SRMs in English, with no limitation of study design. Results: SRMs under AS have a slow growth potential in general. The mean linear growth rate is 0.33 cm/year, the mean volumetric growth rate is 9.48 cm 3 /year. The rate of metastasis during AS is below 2%. Some factors are associated with the growth rate of SRMs, including tumor grade, histological subtype, initial tumor size, age, radiographic characteristics, and molecular markers. No definite predictor of growth rate of SRMs is defined at present. SRMs with high tumor grade and the subtype of clear cell renal cell carcinoma may have aggressive growth potential. Conclusions: AS is a reasonable choice for elderly patients with SRMs, who are at high risk from surgery. Progression during observation is the biggest concern while performing AS. There is no definite predictor of progression for SRMs under AS. Percutaneous renal biopsy providing immunohistological and genic biomarkers may improve the understanding of natural history of SRMs