In the present study, we further showed that FGF9 could induce testosterone and progesterone production in mouse primary and tumor Leydig cells, respectively, through the induction of phospho-Akt, -JNK, -p38, and/or -ERK1/2, which are the downstream components of Ras and MAPK signal transduction pathways. Here, MAPK8 is linked to neoplasm.