Because cancer cells are characterized by hyper-proliferation and given the known role of Piwi proteins and their partner piRNAs in epigenetic regulation [31], [39]–[41], it would be interesting to further examine a functional role for piwi genes during malignant hematpoietic transformation and leukemic progression, with the possibility that aberrant PIWI expression in the blood system can drive progenitors to uncontrolled expansion, at least in part, through an epigenetic mechanism. The gene discussed is PIWIL4; the disease is cancer.