Germ cell development pertains to the stepwise activity of gonadal cells to maintain life cycle progression by transferring their genome onto the next generation. In mammals, the precursors of these germ cells, which are called the primordial germ cells (PGCs), emerge during the start of the gastrulation stage. These PGCs are committed to their cellular fate at the epiblast stage and undergo further development until they reach the gonads. A similar pattern of gene expression has been observed in male germ cell tumors (GCTs), fetal germ cells, as well as pluripotent cells, indicating that GCTs arise from modifications in the normal development of the gonocytes.