To determine whether the discrepancy in the radiologic and pathologic size of renal cell carcinoma influences the final cancer stage.

Renal masses resected from December 1999 to September 2004 were identified using a pathologic database and compared by surgical accession number to an existing clinical renal tumor database to identify those T1 and T2 tumors for which radiologic and pathologic data were available. The tumor histologic features, maximal pathologic diameter, and maximal radiologic diameter were recorded. The percentage of tumor size reduction was then calculated using these data.

Of the 236 renal cancers evaluated, 52% had regressed in size when comparing the pathologic and radiologic sizes. When stratified by histologic subtype, clear cell tumors regressed more often and to a greater degree than those that were chromophobe or papillary. Also, 15 organ-confined tumors were downstaged when comparing the maximal radiologic diameter and the maximal pathologic diameter, and 13 of these were clear cell tumors.

A reduction in kidney tumor size is commonly observed at surgical resection because of a loss of blood flow to the tumor. This tumor size reduction has an impact on the final pathologic stage in organ-confined tumors for which size is the only criterion. The greatest tumor size reduction, and most frequent downstaging, was observed for conventional (clear cell) tumors. We believe this may explain, in part, the worse stage-stratified outcomes for clear cell tumors compared with other tumor types. We propose that renal cancer staging should be determined from accurate measurement of the radiologic size, rather than the pathologic size.