Predominant expression of fibroblast growth factor (FGF) 8, FGF4, and FGF receptor 1 in nonseminomatous and highly proliferative components of testicular germ cell tumours

Nonseminomatous components within testicular germ cell tumors affect patien t prognosis to varying degrees. These components are well known to mimic ea rly embryonic totipotential tissues. Prompted by the recent observation tha t fibroblast growth factor (FGF) 8, FGF4, and FGF receptor (FGFR) 1 are req uired for the growth of early postimplantational embryonic tissues, we inve stigated the expressions of FGF8. FGF4, and FGFR1 in surgically resected sp ecimens of primary testicular germ cell tumors using an immunohistochemical method. All cases of embryonal carcinoma (14 cases), yolk sac tumor (3 cas es), and choriocarcinoma (3 cases) showed positive immunostaining for FGF8, FGF4, and FGFR1. In contrast, out of 13 cases of seminoma, immunostaining was negative for FGF8, FGF4, and FGFR I in 8 cases (61.5%), 6 cases (46.1%) , and 7 cases (53.8%), respectively. In 7 cases of mature and immature tera toma, most areas showed negative immunostaining. In addition, the Ki-67 lab eling index showed extremely high mitogenic activity in embryonal carcinoma , yolk sac tumor, and choriocarcinoma, which are precisely the carcinomas w ith the highest expressions of FGF8. FGF4. and FGFR1. It is in keeping with the immunohistochemical result that murine teratocarcinoma P19 cells were shown to express FGF8, FGF4, and FGFR1 only under undifferentiated growth c onditions. Taken together, these findings confirm the involvement of FGF8, FGF4. and FGFR1 in highly proliferative conditions of nonseminomatous germ cell tumors.