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BACKGROUND: To determine the expected growth rate of renal masses (RM) placed on an active surveillance (AS) protocol, and to illustrate
the clinical outcomes of patients on AS.
METHODS: Our institution prospectively maintains records of patients on AS for RMs, which were reviewed for data on patient demographics and clinical, radiological, and pathologic RM characteristics. Patients were followed at 6-12 month intervals with serial abdominal imaging (CT,MRI, or renal ultrasound), with additional testing selectively performed for patients at risk for progression. Kaplan-Meier analysis was utilized to estimate the annual likelihood of intervention. RMs included in the growth kinetics analysis had >1 year (yr) follow up, and a mixed regression model was utilized to determine the annual linear growth rate. RMs were grouped into 3 radiographic subcategories for analysis (solid enhancing/ no macroscopic fat (solid), angiomyolipoma (AML), and Bosniak ≥IIF cystic).
RESULTS: Data for 151 patients on AS for 168 RMs were available. Median patient age was 67 yrs (range 20-89 yrs), median Charlson Comorbidity Index score was 6, and mean follow up was 3.6 +/- 2.2 yrs (range1-10.3 yrs). The mean tumor maximal diameter for all RMs at diagnosis was 2.1 +/-1.3 cm (solid- 1.9cm (range 0.7-4), AML-1.6cm (0.4-4.6), cystic- 2.9cm (0.9-9.2). 58 RMs exhibited negative or zero net growth on AS, including 30 of 77 solid masses, 8 of 24 AMLs, and 20 of 29 cystic masses. Mean maximal diameter growth rate for all RMs was 1.0 mm/yr (solid- 0.24mm/yr, AML- 2.3mm/yr, cystic- 2.5mm/yr, p<0.01). When stratified by size at diagnosis, growth rates were 0.6mm/yr for tumors <2cm, 0.84mm/yr for RMs 2-3cm, and 0.4mm/yr for tumors >3cm.
Surgical intervention was performed on 12 RMs, including 6 partial nephrectomies, 5 cryoablations, and 1 selective embolization for AML, at
a median time from diagnosis of 5.4 yrs and at a mean tumor size of 3.2cm (1.7cm-6.5cm). The overall estimated 5 and 10 yr freedom from intervention rates were 92.1% and 64.9%, respectively (solid- 88% and 50%, AML and cystic- 100% and 100%). There were no cases of metastatic spread or death from kidney cancer.
CONCLUSIONS: Active surveillance for RMs resulted in a low rate of tumor growth, a low incidence of surgical intervention, and no cases of metastatic progression. Solid enhancing masses grew at a significantly slower rate than cystic masses or AMLs, but were more likely to trigger intervention. AS should be considered for all patients with small RMs.