DHFR and chronic myelogenous leukemia, BCR-ABL1 positive: However, if this holds true with some targeted therapeutics such as trastuzumab or endocrine therapy, there are also other examples of drug resistance associated with overexpression of the target, such as BCR-ABL with imatinib in chronic myeloid leukemias or DHFR with methotrexate in sarcomas [20], [21].