DIFFERENTIAL EXPRESSION OF THE C-KIT PROTOONCOGENE IN GERM-CELL TUMORS

The c-kit proto-oncogene product and its ligand stem cell factor play an important role in haematopoiesis; spermatogenesis, and melanogenesi s. Using an anti-c-kit antiserum raised against a synthetic peptide, w e studied the immunohistochemical expression of the c-kit gene product in 60 germ cell tumours (GCTs) (53 testicular, 7 extragonadal), deriv ed from primary GCTs in 45 cases and metastatic tumours in 15 cases. T wenty-eight out of 28 seminomas showed c-kit membranous staining in th e majority of cells. A similar pattern of expression was seen in intra tubular germ cell neoplasia. Nine out of 29 (32 per cent) non-seminoma s displayed cytoplasmic, but not membranous, c-kit immunoreactivity in occasional cells. In three mixed GCTs, c-kit expression was limited t o the seminoma component. In normal testis, c-kit expression was obser ved in some basal tubular cells, corresponding to undifferentiated spe rmatogonia. These results suggest a role for c-kit in the oncogenesis of GCT, where down-regulation of c-kit might be a critical step during progression from seminomas to non-seminomas. Immunohistochemical anal ysis of c-kit should be considered as a diagnostic aid for GCT and in particular may be helpful in the identification of certain extragonada l seminomas.