Differential expression of RET finger protein in testicular germ cell tumors.

Testicular germ cell cancer is a common cancer in young adults and its incidence has risen dramatically over the past several decades in Western countries. Because RET finger protein (RFP), which belongs to the large B-box RING finger protein family, has been reported to be expressed in different stages of spermatogenesis, we investigated its expression in testicular germ cell tumors. These comprised 13 pure seminomas, five pure non-seminomatous germ cell tumors (NSGCT) and seven mixed germ cell tumors, four of which contained seminomatous component. In normal adult testis, the expression of RFP was strong in the germ cells, particularly in spermatogonia and primary spermatocytes. RFP immunoreactivity was seen uniformly and specifically in 12 of the 13 pure seminomas examined. It was also detected in seminomatous components of mixed germ cell tumors, whereas pure NSGCT were negative for RFP expression. The expression of RFP in male germ cells and seminomas together with the lack of its expression observed in highly aggressive NSGCT suggested that RFP could be associated with the regulation of germ cell proliferation and/or histological-type of germ cell tumors.