Prognostic factors in patients with small renal masses: a comparison between <2 vs. 2.1–4 cm renal cell carcinomas

Background: Few data factually support the prognostic distinction between renal cell carcinomas (RCC) < 2 vs. 2.1–4 cm, in terms of cancer-specific mortality (CSM). We investigated CSM rates over time in <2 vs. 2.1–4 cm RCC, according to patient and tumor characteristics. Methods: Within the Surveillance, Epidemiology and End Results (SEER) database, we focused on patients with T1aN0M0 RCC who underwent either radical or partial nephrectomy between 2000 and 2015. Temporal trends, Kaplan-Meier plots and multivariable Cox-regression analyses assessed CSM. Results: Of 43,147 T1aN0M0 patients, 12,238 (28.4%) harbored RCC < 2 cm and 30,909 (71.6%) 2.1–4 cm RCC. The distribution of histological subtypes according to 2 cm cut-off was as follows: a). clear-cell G1/G2: 64.5 vs. 61.8%; b). papillary G1/G2 15.9 vs. 11.1%; c). clear-cell G3/G4: 9.9 vs. 16.1%; d). papillary G3/G4 4.9 vs. 5.4%; and e). chromophobe 4.9 vs. 5.2%. Five-year CSM rates were invariably lower in RCC < 2 cm than in 2.1–4 cm, for all histological subtypes and grade groups (a-e), even after additional multivariable adjustment for age and residual tumor size differences. 5-year CSM rates improved in more contemporary years, in both tumor size groups (< 2 vs. 2.1–4 cm), but to a greater extent in 2.1–4 cm renal masses. Conclusion: Our results validate the presence of prognostically more favorable CSM outcomes in RCC < 2 cm vs. 2.1–4 cm, across all histological subtypes and grades. Moreover, temporal improvements were also recorded in both <2 and 2.1–4 cm RCC groups, with more pronounced improvements in patients with 2.1–4 cm renal masses. However, prospective randomized trials are needed to further confirm our results.