Validation of the 2009 TNM version in a large multi-institutional cohorts of patients treated for renal cell carcinoma: are further improvements needed?

Background: A new edition of the TNM was recently released that includes modifications for the staging system of kidney cancers. Specifically, T2 cancers were subclassified into T2a and T2b (≤10 cm vs >10 cm), tumors with renal vein involvement or perinephric fat involvement were classified as T3a cancers, and those with adrenal involvement were classified as T4 cancers. Objective: Our aim was to validate the recently released edition of the TNM staging system for primary tumor classification in kidney cancer. Design, setting, and participants: Our multicenter retrospective study consisted of 5339 patients treated in 16 academic Italian centers. Intervention: Patients underwent either radical or partial nephrectomy. Measurements: Univariable and multivariable Cox regression models addressed cancer-specific survival (CSS) after surgery. Results and limitations: In the study, 1897 patients (35.5%) were classified as pT1a, 1453 (27%) as pT1b, 437 (8%) as pT2a, 153 (3%) as pT2b, 1059 (20%) as pT3a, 117 (2%) as pT3b, 26 (0.5%) as pT3c, and 197 (4%) as pT4. At a median follow-up of 42 mo, 786 (15%) had died of disease. In univariable analysis, patients with pT2b and pT3a tumors had similar CSS, as did patients with pT3c and pT4 tumors. Moreover, both pT3a and pT3b stages included patients with heterogeneous outcomes. In multivariable analysis, the novel classification of the primary tumor was a powerful independent predictor of CSS (p for trend <0.0001). However, the substratification of pT1 tumors did not retain an independent predictive role. The major limitations of the study are retrospective design, lack of central pathologic review, and the small number of patients included in some substages. Conclusions: The recently released seventh edition of the primary tumor staging system for kidney tumors is a powerful predictor of CSS. However, some of the substages identified by the classification have overlapping prognoses, and other substages include patients with heterogeneous outcomes. The few modifications included in this edition may have not resolved the most critical issues in the previous version.