BCR and chronic myelogenous leukemia, BCR-ABL1 positive: The expression of PARP1 is upregulated in BCR/ABL+ cells as part of a non-homologous end joining DNA repair pathway (ALT NHEJ) and can serve as biomarker to identify a subgroup of CML patients who may be candidates for therapies that target the ALT NHEJ pathway when treatment with TKIs has failed.36