Is renal sinus fat invasion the same as perinephric fat invasion for pT3a renal cell carcinoma?

Purpose: Perinephric and renal sinus fat invasion are classified as pT3a renal cell carcinoma (RCC) according to the 2002 American Joint Committee on Cancer. We investigated the prognostic significance of each of these pathological features using a cohort of pT3a patients. Materials and Methods: Between 1970 and 2002, 205 patients without direct adrenal invasion underwent nephrectomy for pT3a clear cell RCC. The associations of fat invasion with death from RCC were evaluated using Cox proportional hazards regression models. Results: Of the 162 patients with perinephric fat invasion and 43 patients with renal sinus fat invasion 95 (59%) and 31 (72%), respectively, died of RCC. Patients with renal sinus fat invasion were 63% more likely to die of RCC compared with those with perinephric fat invasion (RR 1.63, 95% CI 1.09-2.46, p = 0.018). In addition, the risk of death persisted in multivariate analysis after adjusting for regional lymph nodes and distant metastases (RR 1.91, 95% CI 1.26-2.89, p = 0.002) and after adjusting for the Mayo Clinic SSIGN (stage, size, grade and necrosis) score (RR 1.90, 95% CI 1.25-2.88, p = 0.003). Conclusions: Our results indicate that clear cell tumors invading the renal sinus fat are more aggressive than tumors with perinephric fat involvement. We believe both of these features should be individually assessed during routine pathological examination. External validation is needed before suggesting a change to the TNM staging system.