Purpose: The 2002 primary tumor classification for renal cell carcinoma (RCC) does not distinguish between patients with tumor thrombus involving the renal vein only and those with inferior vena cava tumor thrombus below the diaphragm. We evaluated the association of tumor thrombus level and fat invasion with outcome to determine if further subclassification would improve the prognostic accuracy of the current classification.
Materials and methods: We studied 675 patients treated with radical nephrectomy or nephron sparing surgery for pT3a (206, 30.5%), pT3b (422, 62.5%), pT3c (19, 2.8%) or pT4 (28, 4.2%) RCC at the Mayo Clinic between 1970 and 2000. Associations with outcome were evaluated using Cox proportional hazards regression.
Results: There were 531 deaths from RCC at a median of 1.5 years following nephrectomy. Patients with pT3b RCC and level I, II or III tumor thrombus were significantly more likely to die of RCC compared to patients with pT3b RCC and level 0 tumor thrombus (risk ratio 1.62, p <0.001). Patients with peripheral perinephric or renal sinus fat invasion were also more likely to die of RCC compared to patients without fat invasion (risk ratio 1.87, p <0.001). Therefore, patients with pT3 RCC were reclassified into 4 groups as thrombus level 0 without fat invasion, fat invasion only, thrombus level 0 with fat invasion or thrombus level I, II or III without fat invasion, and thrombus level I, II or III with fat invasion or thrombus level IV. This reclassification significantly improved prediction of death from RCC compared with the current classification (c indexes of 0.61 versus 0.55, respectively).
Conclusions: Further subclassification of the primary tumor classification for patients with pT3 RCC improved prognostic accuracy.