The extent of tumour fat invasion affects survival in patients with renal cell carcinoma and venous tumour thrombosis.

Objective: • To investigate the effect of presence and extent of tumour fat invasion (TFI) - perinephric invasion (PFI), renal sinus fat invasion (RSFI) or both PFI and RSFI - on cancer-specific mortality (CSM) in patients with renal cell carcinoma (RCC) and venous tumour thrombus (VTT).

Methods: • We examined 184 consecutive patients with RCC with VTT treated with nephrectomy between 1987 and 2007. Associations with CSM were evaluated by univariable and multivariable Cox proportional hazard models.

Results: • Median follow up was 21 months. The 5-year CSM-free survival estimates were 75%, 36% and 20% in patients with VTT without TFI, those with VTT with PFI or RSFI, and those with VTT with both PFI and RSFI, respectively (P < 0.001). In multivariable analyses, presence of either PFI or RSFI was associated with a two-fold increased risk of CSM, whereas presence of both PFI and RSFI was associated with a three-fold increased risk of CSM, relative to VTT-only cases. • The inclusion of the variable describing the presence and extent of TFI in a base model including pT stage, Fuhrman grade and presence of nodal disease and metastatic disease significantly increased the accuracy in predicting CSM (+2.1%; P < 0.001) in patients with VTT.

Conclusions: • Patients affected by RCC with VTT and TFI have a higher risk of CSM relative to cases with VTT only. Patients with both PFI and RSFI showed increased CSM compared with patients with either PFI or RSFI. • Our results suggest TFI should be accurately evaluated and included in routine pathological reports to provide better patient risk stratification.