Immunohistochemical expression of the KIT protein (CD117) in normal and neoplastic canine testes

The aim of the present study was to characterize the expression of the KIT protein (CD117) in normal and neoplastic canine testes. Archival samples of normal testis (n 5), interstitial cell tumours (ICTs; n 10), Sertoli cell tumours (SCTs; n 10) and seminomas (n 10) were selected. Seminomas were subclassified on the basis of expression of placental alkaline phosphatase (PLAP) as classical seminoma (SE; PLAP positive; n 5) or spermatocytic seminoma (SS; PLAP negative; n 5). In normal testes, KIT expression was observed in Leydig cells and in spermatogonia. All ICTs expressed KIT, but no SCT was positively labelled. Seven of 10 seminomas expressed KIT and these tumours were reclassified on this basis as SS (KIT negative) or SE (KIT positive). These findings are consistent with observations of SE in man where many of the neoplastic cells reach the stage of spermatogonia where PLAP expression is lost and that of KIT is maintained. It would therefore appear that immunolabelling for KIT expression is a more appropriate means of distinguishing between canine SE and SS.