We previously reported the expression of protooncogene c-kit in CNS germ cell tumors and suggested that the soluble form of c-kit (s-kit) may represent a specific clinical marker for germinoma-containing tumors. Here we investigated the expression of stem cell factor (SCF), a specific ligand of c-kit, in CNS germ cell tumor samples from 16 patients, using immunohistochemical methods to assay the expression of c-kit and SCF protein. The immunostaining patterns of c-kit and SCF were almost identical. In all germinoma-containing tumors, c-kit and SCF were diffusely expressed on the surface of germinoma cells
lymphocytes and interstitial cells were negatively stained. In immature teratomas, only some mature components, e.g., cartilage and gland, were immunoreactive for c-kit and SCF. Syncytiotrophoblastic giant cells (STGCs) were negative for both SCF and c-kit, suggesting that germinoma cells primarily coexpress SCF and c-kit. The coexpression of c-kit and SCF may be an important immunohistochemical marker for the diagnosis of CNS germinoma, and the SCF/c-kit pathway may be an alternative molecular target for the treatment of human CNS germinomas.