Imatinib was the very first small molecule inhibitor approved by the FDA in 2001 for use in chronic myelogenous leukaemia (CML).154,155 Imatinib targets PDGFR, BCR-ABL and c-KIT, making it one of several multi-targeting RTK inhibitors on the market, and is the gold-standard for treating CML and gastrointestinal stromal tumours (GISTs). Here, PDGFRB is linked to chronic myelogenous leukemia, BCR-ABL1 positive.