Our prior report on the significant temporal delay in the development of CML upon the transplantation of BMDC cells from SOS1-KO mice that were retrovirally infected with a p210BCR/ABL construct into irradiated recipient mice [17] provided indirect evidence suggesting the participation of SOS1 in the process of CML development. The gene discussed is SOS1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.