Active Surveillance of Renal Masses: An Analysis of Growth Kinetics and Clinical Outcomes Stratified by Radiological Characteristics at Diagnosis

Aims: To determine the growth rate of renal masses (RMs) under active surveillance (AS), and to describe the clinical outcome of AS patients. Materials and Methods: We conducted a retrospective review of an AS database to obtain demographics, radiological and pathologic characteristics and RM size of patients. RMs were followed at 6-12 month intervals for >= 1 year with computed tomography (CT), magnetic resonance imaging (MRI), or renal ultrasound. Kaplan-Meier analysis determined the annual likelihood of intervention. RMs were divided into 3 radiographic subcategories (solid, cystic, and angiomyolipoma). A linear regression model determined RM growth rates. Results: 131 RMs in 114 patients were included. Median age, Charlson Comorbidity Index score and mean follow-up were 69.1 years, 4.0 and 4.2 +/- 2.6 years, respectively. Maximal tumor diameter (MTD) at diagnosis was 2.1 +/- 1.3 cm. 49 RMs exhibited negative or zero net growth. Mean MTD growth rate for all RMs was 0.72 +/- 3.2 (95% CI: 0.16-1.28) mm/year. When stratified by MTD at diagnosis, mean RM growth rates were 0.84, 0.84, 0.44, 0.74 and 0.71 mm/year for RMs <1 cm, 1-<2cm, 2-<3cm, 3-<4cm and = 4cm, respectively (p<0.01). The 5 and 10-year freedom from intervention rates were 93.1% and 88.5%, respectively. There was a single case of suspected metastases, but no deaths related to kidney cancer. Conclusions: RMs under AS grew slowly, and had a low incidence of requiring surgical intervention and progression. Solid enhancing masses grew slowly, and were more likely to trigger intervention. AS should be considered for selected patients with small RMs.