Robot-assisted partial nephrectomy (RAPN) treatment of renal cell carcinomas (RCCs) is limited to smaller masses, due to increase in technical difficulties with masses>4cm (cT1b). This study aims to assess perioperative, functional and oncological outcomes of patients with cT1b vs cT1a RCCs.

This study retrospectively reviewed 161 consecutive patients (age 57±12, n(male)=104) who underwent RAPN between Jan 2021 to April 2024 at the National University Hospital, Singapore. 130 patients were cT1a RCC and 31 were cT1b based on pre-operative imaging. Relevant baseline, peri and post-operative outcomes were compared. Median follow-up was 27.5 months.

There was no significant difference (p>0.05) between cT1b and cT1a in terms of mean age (57.7±13 vs 56.9±12), male gender (58% vs 66%), ASA 1-2 (84% vs 83%) and left sided tumours (45% vs 46%). As expected, mean tumour size was larger (4.9±0.64 vs 2.4±0.83mm,p<0.001) and proportion of high tumour complexity by RENAL nephrometry score was greater (4% vs 13%,p<0.001) in cT1b vs cT1a. Peri-operatively, cT1b RAPNs were associated with longer operation time (284 vs 244min,p=0.003), warm ischemia time (29 vs 23min,p=0.002) and greater blood loss (243 vs 133ml,p=0.004) compared to cT1a respectively. Pathologically, they were also more likely upstaged to pT3a (35% vs 5%,p<0.001) and had higher WHO/ISUP grading of 3-4 (55% vs 43%,p=0.03). Despite increased technical challenges, robot assistance facilitated 0% complications (Clavien-Dindo≥3) with comparable positive pathological surgical margins between cT1b vs cT1a (6% vs. 8%,p=1.0). At 1-year follow up, 100% of cT1b patients survived with no recurrence and eGFR decline was equivalent to cT1a patients. 22 of the 31 cT1b patients completed 2-year follow up with no local recurrence but 2(6%) developed distant metastasis.

RAPN can be electively performed for cT1b RCCs with equivalent outcomes to cT1a RCCs, despite greater technical difficulties and a higher risk of pathological upstaging.