Objective: The objective of this study was to evaluate the early surgical outcomes of robot-assisted partial nephrectomy (RAPN) for small renal masses in a large Japanese multicenter series. Methods: A total of 804 consecutive cases of RAPN were examined at 42 institutes between 2011 and 2016. Medical records for clinical, pathological characteristics and perioperative outcomes were retrospectively reviewed. Univariable and multivariable analyses were performed to determine factors predicting Trifecta achievement. Results: The median tumor size was 2.6 cm. The median RENAL score was 7. The median warm ischemia time was 21 min. The median estimated blood loss was 30 mL. Eight patients (1.0%) were converted to radical nephrectomy. The overall and Clavien–Dindo grade ≥ 3 complication rates were 13.0% and 5.8%, respectively. Pathologically, 91.4% of tumors were malignant and the positive surgical margin (PSM) rate was 1.1%. During the median 27.1-month observation period, the recurrence rate was 1.6%. Postoperative preservation rates of eGFR at 1, 6, 12 and 24 months were 90.3, 89.8, 89.4 and 89.2%, respectively. Trifecta was achieved in 62.1%. Multivariable analysis demonstrated that tumor diameter, estimated blood loss and hilar location of the tumor were significant negative factors predicting Trifecta achievement. The rate of Trifecta achievement for T1b tumors and hilar tumors was significantly lower (48.4% and 50.0%, respectively). Conclusions: RAPN was safely performed with acceptable oncological and functional outcomes, but the rate of Trifecta accomplishment for T1b or hilar tumors was significantly lower than that for T1a or non-hilar tumors, respectively.
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