KIT expression in chromophobe renal cell carcinoma: comparative immunohistochemical analysis of KIT expression in different renal cell neoplasms.

The overexpression of c-Kit in chromophobe renal cell carcinoma (ChRCC) has been described by comparative gene expression analyses and has been proposed as a possible specific hallmark of this neoplasm. The aim of our study was to establish its immunohistochemical expression in a large series of ChRCC and to compare it with other renal neoplasms. In our study, immunohistochemical characterization of KIT was performed in 87 renal neoplasms including 25 cases of ChRCC, 13 cases of renal oncocytoma, and 39 renal cell carcinomas (21 cases of conventional RCC [CRCC], 8 cases of CRCC with granular cell differentiation, and 10 cases of papillary RCC [PRCC]). Eighty-eight percent ChRCC and 71% oncocytomas showed immunohistochemical expression of KIT, while the other types of RCC studied were all negative. The meaning of immunohistochemical expression of KIT in ChRCC and oncocytomas is still unknown, but its immunohistochemical staining appears to be useful in distinguishing ChRCC from PRCC, CRCC, and its granular cell variant. Moreover, our findings support current models that consider that there is a histopathogenic relationship between oncocytoma and ChRCC. Finally, it should be determined whether KIT plays a role in the tumorigenesis of ChRCC and oncocytoma and whether targeted therapy with STI-571, an inhibitor of KIT, could be effective in exceptional cases of ChRCC with metastatic extension or recurrence.