Is anatomic complexity associated with renal tumor growth kinetics under active surveillance?

Introduction: Linear growth rate (LGR) is the most commonly employed trigger for definitive intervention in patients with renal masses managed with an initial period of active surveillance (AS). Using our institutional cohort, we explored the association between tumor anatomic complexity at presentation and LGR in patients managed with AS. Methods and materials: Enhancing renal masses managed expectantly for at least 6 months were included for analysis. The association between Nephrometry Score and LGR was assessed using generalized estimating equations, adjusting for the age, Charlson score, race, sex, and initial tumor size. Results: Overall, 346 patients (401 masses) met the inclusion criteria (18%≥cT1b), with a median follow-up of 37 months (range: 6-169). Of these, 44% patients showed progression to definitive intervention with a median duration of 27 months (range: 6-130). On comparing patients managed expectantly to those requiring intervention, no difference was seen in median tumor size at presentation (2.2 vs 2.2 cm), whereas significant differences in median age (74 vs 65 y, P<0.001), Charlson comorbidity score (3 vs 2, P<0.001), and average LGR (0.23 vs 0.49 cm/y, P<0.001) were observed between groups. Following adjustment, for each 1-point increase in Nephrometry Score sum, the average tumor LGR increased by 0.037. cm/y (P = 0.002). Of the entire cohort, 6 patients (1.7%) showed progression to metastatic disease. Conclusions: The demonstrated association between anatomic tumor complexity at presentation and renal masses of LGR of clinical stage 1 under AS may afford a clinically useful cue to tailor individual patient radiographic surveillance schedules and warrants further evaluation.