Notable examples include the emergence of T790M mutation in epidermal growth factor receptor (EGFR) leading to resistance to gefitinib in EGFR-mutant lung cancer[4], T315 in ABL1 causing imatinib/dasatinib resistance in acute lymphocytic leukemia and CML[5,6]; and ERBB2/HER2 truncation leading to trastuzumab resistance in ERBB2-positive breast cancer[7]. The gene discussed is ERBB2; the disease is acute lymphoblastic leukemia.