Son of sevenless homolog 1 (SOS1) is an essential guanine nucleotide exchange factor (GEF) in KRAS-driven tumors, and it also functions as a downstream node protein of BCR-ABL, suggesting its critical role in the pathogenesis of chronic myeloid leukemia (CML). Investigators at Shanghaitech University have reported the discovery and preclinical characterization of a novel potent SOS1 proteolysis targeting chimera (PROTAC) – SIAIS-562055 – being developed as an anticancer agent.