Regarding tumoral pathogenesis, our earlier studies of SOS1- and/or SOS2-knockout mice also suggested the critical contribution/participation of SOS1 in the development of RAS-dependent, DMBA/TPA chemically induced skin tumors [31] and Bcr/Abl-driven chronic myeloid leukemia (CML) [17]. This evidence concerns the gene SOS2 and chronic myelogenous leukemia, BCR-ABL1 positive.