Enhancing renal masses with zero net growth during active surveillance

Purpose: The natural history of small renal masses is generally to slowly increase in size. However, a subset of lesions does not show radiographic growth. We compared clinical, radiographic and pathological characteristics of enhancing renal masses under active surveillance with zero net radiographic growth vs those with positive growth. Materials and Methods: We identified 106 enhancing renal masses that were observed for 12 months or greater. Lesions were grouped according to growth characteristics. Group 1 consisted of lesions demonstrating zero or negative growth. Group 2 tumors showed positive growth during surveillance. Clinical, radiographic and pathological parameters were then compared. A MEDLINE (R) search was performed regarding zero growth lesions during observation for suspected renal cell carcinoma in the world literature. Results: Group 1 consisted of 35 lesions (33%) with a median growth rate of 0.0 cm yearly. Group 2 included 70 lesions (67%) showing growth at 0.31 cm yearly (p < 0.0001). No differences were detected with regard to patient age (p = 0.96), lesion size (p = 0.41), solid/cystic appearance (p = 1.00) or the incidental detection rate (p 0.38). While 17% of group 1 lesions (6 of 35) underwent intervention, 51% (36 of 71) in group 2 were ultimately treated (p = 0.001). Pathological assessment showed a similar incidence of malignancy in groups 1 and 2 (83% and 89%, respectively, p = 0.56). A literature review revealed that 78 of 295 observed lesions (26%) failed to demonstrate radiographic growth. Conclusions: We were unable to identify definable clinical characteristics to predict the future growth of enhancing renal masses under active surveillance. Our analysis demonstrated that 26% to 33% of these tumors do not demonstrate growth at 29 months median follow up. These lesions have similar rates of malignancy compared to growing lesions and rates of progression to metastatic disease are similarly low. A brief period of active surveillance may be feasible with treatment limited to lesions that increase in size.