Pathologic characteristics of exophytic renal masses

Pathologic grade is an important prognostic factor for renal-cell carcinoma (RCC). The objective of this study was to determine if there is any association of radiologic characteristics with pathologic grade and type of small renal tumors.

We retrospectively reviewed the records of 500 patients who underwent extirpative renal surgery. Fifty-one patients met the inclusion criteria of solitary RCC <6 cm and adequate radiologic imaging available for review. The axial images with the largest area of tumor growing into the kidney were evaluated by a single radiologist to determine the percent of tumor that was exophytic.

Nine patients had tumors that were >67% exophytic, and 42 patients had tumors <67% exophytic. There is a statistically significant difference in the mean Fuhrman grade for these 2 groups (1.78 v 2.25, P < 0.01). The distribution of histologic subtype was as follows: 34 patients with clear cell, 15 with papillary, and one each with chromophobe and unclassified tumors. Papillary RCC comprised 78% (7 of 9) of tumors that were >67% exophytic and 15% (3 of 20) that were <33% exophytic. The relative risk of a >67% exophytic tumor being papillary v nonpapillary is 4.1.

Exophytic renal tumors are more likely to be of lower pathologic grade and of the papillary RCC subtype when compared with endophytic renal tumors. A larger prospective study is required to confirm these findings and determine the implications. This information may be useful when small tumors are being considered for watchful waiting or ablative therapies.