Optimal margin in nephron-sparing surgery for renal cell carcinoma 4 cm or less

Renal cell carcinoma (RCC) of 4 cm or less is with a low incidence of multicentricity and metastasis and is usually considered suitable for nephron-sparing surgery (NSS). This study was designed to investigate the distance between extra-pseudocapsule cancer lesions and primary tumors, and to suggest the optimal margin of normal parenchyma in NSS for RCC 4 cm or less.

We prospectively studied 82 kidneys in which RCCs of 4 cm or less were resected by radical nephrectomy. According to UICC TNM classification (1997), all tumors were staged as T1 and classified as conventional RCC in 76 cases and papillary RCC in 6 cases. The kidney samples were first step sectioned at 3mm intervals and examined for multicentricity. Then, on each layer of tissue sectioned, parenchyma margins of 15 mm beyond pseudocapsule were continuously sectioned and examined microscopically to investigate completeness of pseudocapsule and possible presence of extra-pseudocapsule cancer lesions. The greatest distance between extra-pseudocapsule lesions and primary tumors was measured.

The diameter of 82 primary tumors was 3.4+/-0.7 mm (range 1.5-4.0 cm). Of them, 31.7% (26/82) were found without intact pseudocapsule. Of the 82 cases, 19.5% (16/82) were with positive cancer lesions beyond pseudocapsule, with invasion into normal parenchyma in 12.2% (10/82), into venule in 2.4% (2/82) and satellite tumors in 4.9%(4/82). The average distance between extra-pseudocapsule cancer lesions and primary tumors was 0.5+/-1.3mm (range 0-5.0mm), with a 95% confidential interval (CI) (0.11, 0.94). No significant difference was found in the incidence of extra-pseudocapsule cancer lesions between the tumors 2.5 cm or less and that greater than 2.5 cm.

These data suggest that when partial nephrectomy is performed in RCC 4 cm or less, a 10mm margin may be too large and go against renal function maintaining. Enucleation alone was associated with a significant risk of incomplete excision, and therefore liable for local recurrence. Thorough inspection of the whole kidney before and during operation may help to avoid leaving over large and distant multifocal lesions.