Natural history of small renal cell carcinoma: Evaluation of growth rate, histological grade, cell proliferation and apoptosis

Purpose: We investigated the natural history of incidentally discovered small renal cell carcinomas (RCCs), and we evaluated growth rate, apoptosis, cell proliferation and histological grade. Materials and Methods: A total of 18 patients with RCCs extirpated after at least 12 months of observation were reviewed retrospectively. The period of observation ranged from 12 to 63 months (median 22.5). Median patient age was 56.5 years, ranging from 37 to 71. Annual tumor growth rate was calculated from diameter obtained from computerized tomography or ultrasound. Cell proliferation and apoptosis were assessed by immunostaining using Ki-67 and TUNEL. Results: Average tumor growth rate was 0.42 cm per year (standard error 0.09, 95% confidence interval 0.24 to 0.61). Of the 18 tumors 7 were grade 1, 8 were grade 2 and 3 were grade 3. Tumor growth rate and Ki-67 positive ratio were not correlated. In contrast, growth rate and positive ratio of TUNEL were significantly correlated. A significant difference in growth rate was observed between grade 2 and 3 tumors but not between grade 1 and 2 tumors. Conclusions: The growth rate of RCCs correlates with apoptosis and grade. Most incidentally found RCCs are slow growing. However, those with certain histopathological features can grow rapidly and have a poor prognosis. More attention should be given to the observation of small renal masses.