The 4-cm Rule in Partial Nephrectomy: Analysis of Surgical Selection and Safety Using Japan's National Clinical...

Tumor size is a crucial prognostic factor in renal cell carcinoma (RCC). The traditional 4-cm cutoff in the tumor-node-metastasis classification was established for oncological prognosis rather than technical feasibility or perioperative safety. This study examined the relationship between tumor size, surgical selection, and perioperative outcomes to reassess the role of this threshold in contemporary practice.

We conducted a retrospective cohort study using Japan's National Clinical Database, including patients undergoing partial nephrectomy (PN) or radical nephrectomy for T1 RCC during 2018 to 2021. Complete-case multivariable logistic regression with generalized estimating equations assessed factors associated with PN selection and 30-day outcomes free from complications or death after PN. Restricted cubic splines were used to examine nonlinear associations with tumor size.

Among 36,015 patients in 941 hospitals, including 22,860 undergoing PN, tumor size showed a continuous, near-linear inverse association with the odds of PN selection, without a distinct threshold at 4 cm. Among PN cases, the adjusted odds of remaining free from complications or death decreased with increasing tumor size up to approximately 5 cm, with an apparent plateau thereafter.

Tumor size remains important for technical assessment and oncological risk stratification, but the 4-cm cutoff alone is insufficient to guide PN selection. Tumor size was continuously associated with surgical choice, while the apparent safety plateau beyond approximately 5 cm among selected PN cases warrants cautious interpretation. Individualized decision-making should integrate tumor size with anatomical complexity, patient factors, and surgical expertise.