Histological reclassification, histochemical characterization and c-kit immunoexpression in renal cell carcinoma

Renal cell carcinoma is the most lethal of all urologic malignancies. Several parameters such as histological subtype, nuclear grade and TNM staging help in determining the prognosis and treatment options. A newer therapeutic modality has been suggested based on expression of c-kit antigen by the tumor cells. This study was designed to evaluate various histological parameters and correlate them with c-kit expression.

The study was done on 40 consecutive cases of renal epithelial tumors. Histological sections were reviewed and reclassified according to WHO (2004) classification and nuclear grade assessed. Hale's colloidal iron stain was done to identify the chromophobe variant. Immunostaining with c-kit was done and its expression was studied. The results were correlated and statistical significance was assessed.

The age range was 31-81 years, with a male to female ratio of 2:1. Seventy per cent of the cases were clear cell RCC (ClRCC), 17.5% were chromophobe type, 7.5% were papillary RCCs and 5% cases were oncocytomas. Fuhrman nuclear grading revealed 60.5% cases to be of low grade and 39.5% high grade. Hale's colloidal iron staining was positive in chromophobe RCC and oncocytomas, while it was negative in ClRCC. Immunostaining with c-kit was positive only in oncocytomas.

Clear cell RCC was the most common histological subtype of RCC. Clear cell RCC known to have a poor prognosis, showed a statistically significant higher nuclear grade than chromophobe and papillary RCCs which have a better prognosis. Hale's colloidal iron staining was extremely useful in distinguishing chromophobe RCC and oncocytoma from the granular cell variant of clear RCC. Our study revealed c-kit negativity in all RCC. As Imatinib could be ineffective in such tumors, its clinical activity has to be carefully assessed in such tumors through further studies.