A previous in vitro study revealed that miR-17-92 is highly expressed in THY1+-enriched undifferentiated spermatogonia, and the members of miR-17-92 cluster are remarkably downregulated during in vitro retinoic acid (RA)-induced spermatogonial differentiation.15 miR-17-92 has been demonstrated to positively regulate the self-renewal and proliferation of cancer stem cells,55,56 hematopoietic and neural stem cells.57–59 These findings suggest that miR-17-92 cluster may play important roles in SSC self-renewal and proliferation of the undifferentiated spermatogonia. The gene discussed is THY1; the disease is cancer.