Robotic-assisted Partial Nephrectomy for "Very Small" (<2 cm) Renal Mass: Results of a Multicenter Contemporary Cohort

Background: Patient with "very small" (<2 cm) renal mass can be offered active surveillance, thermal ablation, or partial nephrectomy. The management strategy will consider patient preferences and prioritize potential harms associated with each of these options. To date, outcomes of robot-assisted partial nephrectomy (RAPN) in patients with "very small" renal masses have not been reported.

Objective: To assess the outcomes of RAPN among patients with "very small" renal masses.

Design, setting, and participants: This was a retrospective analysis of a multi-institutional database including RAPN cases performed at eight high-volume US and European centers between 2009 and 2019. Patients were stratified into two groups according to clinical tumor size: <2 cm ("very small" renal mass, study group) and 2-4 cm (control group).

Intervention: RAPN for renal masses.

Outcome measurements and statistical analysis: Baseline characteristics and intraoperative, pathological, and postoperative data were compared between the study and the control group. A "trifecta" was used as surrogate of "surgical quality."

Results and limitations: Overall, a total of 1019 patients were included in the analysis. Of these, 352 had a renal mass of <2 cm (34.5%) and 667 (65.5%) had a renal mass of 2-4 cm. At baseline, the study group presented a lower rate of chronic kidney disease ≥stage III (p < 0.001), a lower RENAL score (p = 0.001), and lower rates of hilar (p = 0.04) and endophytic (p = 0.02) masses. Warm ischemia time was shorter for the study group (median 14 vs 18 min, p < 0.001), which also showed a lower rate of overall postoperative complications (9.6% vs 14.7%, p < 0.001) and no major complications. In terms of oncological outcomes, three and ten patients developed a local recurrence in the study and the control group, respectively (p = 0.1). In the study group, higher estimated glomerular filtration rates were found at discharge (p = 0.001) and at the last follow-up (p = 0.007), which showed a "trifecta" achievement of 90.6%. The retrospective design may limit the generalizability of the findings.

Conclusions: Whenever an active treatment is indicated or warranted, RAPN represents a minimally invasive management option for "very small" renal masses, as it carries minimal risk of complications and has minimal impact on renal function. While both active surveillance and kidney ablation remain valid management options in these cases, RAPN can be offered and discussed with patients as it provides excellent outcomes with low morbidity.

Patient summary: In this report, we observed that robot-assisted partial nephrectomy represents a true minimally invasive active treatment for "very small" renal masses (<2 cm), as it carries minimal risk of complications and has minimal impact on renal function.