Aims: Invasion of perinephric tissues is part of the Union Internationale Contre le Cancer (UICC) (1997) T staging criteria for renal cell carcinoma (RCC) and appears to confer a worse prognosis. However, there are no established histological criteria to determine if this has occurred and histopathologists differ in their interpretation of the tumour margin. The purpose of this study was to determine histological criteria for invasion of perinephric tissues that may be used in staging.
Methods and results: We assessed the prognostic implications of different margin types in 176 cases of RCC with good follow-up data. The tumour margin type in each cases was classified as follows: fibrous tumour capsule; rim of kidney; fibrous capsule with 'collar stud' invasion; pushing margin, no capsule; and tumour cell invasion of fat. The margin types were used in univariate and multivariate survival analysis to determine which had most impact on disease-free survival. In Cox regression analysis with all other influential covariates cellular invasion of fat was the only margin type that had any prognostic impact, conferring a 2.9 relative hazard compared with tumours with a fibrous capsule (P = 0.007).
Conclusions: For staging purposes the designation of a tumour as invading perinephric tissues should be limited to those cases that have tumour cells invading the perinephric fat.