Tumour size is associated with growth rates of >0.5 cm/year and delayed intervention in small renal masses in patients on active surveillance.

Objective: To evaluate the association between tumour size and the growth rate (GR) of small renal masses (SRMs) in patients managed by active surveillance (AS).

Materials And Methods: We queried the prospective, multi-institutional Delayed Intervention and Surveillance for Small Renal Masses (DISSRM) registry for patients on AS with an imaging interval of ≥6 months, identifying 456 patients. We tracked tumour size over time; a GR >0.5 cm/year was defined as a GR event. We used multivariable recurrent events and time-to-event Cox regression modelling to evaluate the association between tumour size and GR events (primary outcome) and tumour size and delayed intervention (DI; secondary outcome). We tested tumour size as a continuous variable and dichotomised tumour size by predefined (2-cm) and calculated (2.9-cm) cutoffs. We calculated the cutoff using maximally selected rank statistics and time to progression, defined according to the DISSRM registry.

Results: The median (interquartile range) follow-up of patients on AS was 40.1 (26.4-71.2) months, during which 128 patients (28%) had ≥1 GR event, and 80 (18%) underwent DI. Larger tumour size was an independent predictor for GR events and DI when tested as a continuous and a dichotomous variable in multivariable analyses (all P < 0.05). The association was strongest when accounting for the change in tumour size over time and when applying the 2.9-cm cutoff. The study is limited by the mixed tumour pathology inert to SRMs.

Conclusion: Larger tumour size was independently associated with GR events and DI for patients with SRMs on AS. A 2.9-cm cutoff may provide valuable information for patient counselling.