In summary, the work here, using an in vitro model of the mouse prepubertal testis, shows that the three chemotherapy drugs CYP (through use of its active metabolite PM), CIS and DOX each induced a rapid and marked decrease in the germ cell population after exposure to clinically relevant concentrations, and that this includes a decrease in the stem germ cell population. Here, PPIG is linked to in situ carcinoma.