The histopathological heterogeneity of small renal cell carcinoma

Renal tumors resembling renal cell carcinoma but less than 3 cm in diameter historically have been regarded as adenomas because of their low frequency of metastases. However, this concept has been challenged, and it seems that all of these lesions should be considered carcinomas. Thus, the extent of radical surgery of these findings have been reconsidered, in view of the uncertainty regarding their malignant or benign nature.

107 tumors 40 mm or less in diameter were accordingly divided into three groups and clinico- and histopathological criteria were correlated: group 1: 20 mm or less (n = 33), group 2: 21-30 mm (n = 28) and group 3: 31-40 mm (n = 43).

Both lymph node metastases and distant metastases were well correlated with tumor size. Grade 1 renal cell carcinomas decreased in their frequency with an increasing tumor diameter. In grade 3 carcinomas an opposite result was found. With an increase of tumor size the frequency of venous involvement increases as well. Significant more multifocal malignant renal cell carcinoma were seen in renal cell carcinoma between 21-40 mm compared to tumors 20 mm or less in diameter.

Although the metastatic potential and the biology of small renal tumors are not yet known, it seems that nephron-sparing surgery in patients with renal cell carcinoma more than 20 mm in diameter should only be performed when there is an absolute indication, such as bilateral carcinomas, single kidney or renal failure. The problem is that a long-term follow-up study is mandatory to justify partial nephrectomy as a nephron-sparing operation for renal cell carcinoma more than 20 mm in patients with normal function of the contralateral kidney.