FACTORS INFLUENCING THE DEVELOPMENT OF TUMOR CAPSULE FORMATION IN CLEAR CELL RCC TREATED WITH NEPHRON-SPARING SURGERY

Aim of the study The capsule around renal cell carcinoma (RCC) represents the first barrier against tumor cells invasion into the kidney and perirenal fat. The aim of the present study is to evaluate tumor capsule thickness in clear cell RCC, and search for any correlation with the main pathologic variables. Materials and methods Between September 2005 and December 2007, data were gathered prospectively from 201 consecutive patients who had open NSS. All specimens were assessed by two dedicated uropathologists. Patients with histologically confirmed benign tumors (26, 12.9%) and those with multiple ipsilateral (4, 2%) and synchronous bilateral RCCs (1, 0.5%) were excluded from the study. The following parameters were evaluated: pathologic tumor diameter, TNM stage, Fuhrman nuclear grade, histotype and the status of tumor capsule. Tumor capsule thickness was measured at the four corners of the sampling (inner and outer pole and equatorial junctions). Results Mean (IQR) maximum tumor diameter was 3.5 (2.4-4.1) cm. At the pathologic examination, 120 over 170 (70.5%) were clear cell RCC. The peritumoral capsule status analysis was focused on patients with clear cell RCC. Overall, in 78 clear cell RCC (64.9%) the capsule was intact and free from invasion (PC-), while in 42 (35.1%) there were signs of penetration within its layers, with or without invasion beyond it (PC+). Complete data on tumor capsule thickness were available for 104 patients. Mean tumor capsule thickness at the inner pole of the tumor (SD, median, range) was 412 μm (250, 350, 20-1511). Mean tumor capsule thickness at the outer pole of the tumor (SD, median, range) was 385 μm (253, 358, 20-1770). In 35 cases (21%) a pericapsular tumor lymphocytic infiltration (TIL) was present. At univariate analysis, thickness of tumor capsule did not significantly correlate with PC+, neither with tumor size, TNM stage, nuclear grade, tumor necrosis or TIL. The capsule thickness measurements were significantly different among the four evaluated points in each single tumor, showing a decreasing thickness from the parenchimal pole to the perinephric pole (p<0.0008). At the analysis of covariance, pathologic maximum tumor diameter did not influence tumor capsule growth for each topographic determination (p=0.359). Discussion There are no extensive data on the possible role of tumor characteristics for the development of tumor capsule formation in clear cell RCC. Conclusions The capsule thickness presents significant variations among the four evaluated anatomical corners in each single tumor, with a greater development in the inner pole of the tumor, thus hypothesising a specific role of healthy parenchyma for its formation. We did not found a significant correlation between thickness of PC and the main pathologic variables of RCC. Moreover, thickness of PC do not influence the risk of its infiltration by the tumor, showing that a thin capsule is not associated with a higher risk of invasion by the tumor.