Compared to T1a lesions the natural history of untreated renal masses larger than 4 cm is poorly understood. We assessed the growth kinetics and outcomes of cT1b/T2 cortical renal tumors managed by an initial period of active surveillance. We compared these cases to those treated with definitive delayed intervention.

We reviewed our institutional, prospectively maintained renal tumor database to identify enhancing solid and cystic masses managed expectantly. Included in analysis were clinically localized tumors greater than 4.0 cm (T1b or greater) that were radiographically followed for more than 6 months. Tumor size at presentation, annual linear tumor growth rate, Charlson comorbidity index, followup and clinical outcomes were compared in patients who remained on active surveillance and those who underwent delayed surgical intervention.

We identified 72 tumors 4 cm or greater in diameter in a total of 68 patients. Active surveillance was the only treatment in 45 patients (66%) while 23 (34%) progressed to intervention. Median tumor size at presentation was 4.9 cm and the mean linear growth rate was 0.44 cm per year. Of the masses 14.7% demonstrated no growth with time. Comparing patients treated exclusively with active surveillance and those who progressed to definitive intervention revealed no difference in median tumor size at presentation (4.9 vs 4.6 cm, p = 0.79) or the median Charlson comorbidity index (3 vs 2, p = 0.6) but significant differences were seen in median age at presentation (77 vs 60 years, p = 0.0002) and the mean linear growth rate (0.37 vs 0.73 cm per year, p = 0.02). After adjustment younger patients (OR 0.91, 95% CI 0.86–0.97) and tumors with a faster linear growth rate (OR 9.1, 95% CI 1.7–47.8) were more likely to be treated with delayed surgical intervention. At a mean ± SD 38.9 ± 24.0 months of followup (median 32, range 6 to 105) 9 patients (13%) had died of another cause and none had progressed to metastatic disease.

Localized cT1b or larger renal masses show growth rates comparable to those of small tumors managed expectantly with a low rate of progression to metastatic disease at short-term followup. An initial period of active surveillance to determine tumor growth kinetics is a reasonable option in select patients with significant competing risks and limited life expectancy.