Reassessment of T1a cutoff for kidney cancer in the robotic era

In 2002, the renal cancer T classification was revised by dividing T1 into T1a and T1b at a 4 cm cutoff. However, local treatment using minimally invasive procedures resulted in better outcomes for tumors smaller than 3 cm, leading the European Association of Urology guideline committee to propose a 3 cm cutoff for T1a/b. Nonetheless, the impact of changing the T1 cutoff on robot-assisted partial nephrectomy (RALPN) has not been fully investigated. This study included 300 out of 335 patients with clinical stage T1 disease who underwent RALPN at our institution between November 2013 and April 2024. We evaluated the discriminative performance of clinical outcomes in each group using tumor diameter cutoffs of 4 and 3 cm. Using a 3 cm cutoff, patients with tumors ≥ 3 cm showed a greater decline in estimated glomerular filtration rate (eGFR) (-9.6% vs. -4.9%, p = 0.003) and a higher incidence of complications (25% vs. 15%, p = 0.040) compared to those with smaller tumors. With a 4 cm cutoff, differences in eGFR decline (-7.8% vs. -6.7%, p = 0.134) and complications (27% vs. 17%, p = 0.100) were not significant. The 3 cm cutoff more accurately predicted complications with a higher area under the curve (0.575 vs. 0.451, p = 0.037). A 3 cm cutoff for the T classification of kidney cancer may more accurately predict postoperative renal function and the risk of complications.