TOP2A and chronic myelogenous leukemia, BCR-ABL1 positive: For example, Wang and co‐workers used a pooled lentiviral library (73 000 sgRNAs) to perform a positive selection screen in KBM7 human chronic myelocytic leukemia (CML) cells and HL60 acute myelocytic leukemia (AML) cells, and identified two genes involved in DNA mismatch repair, TOP2A and CDK6, the loss of which confers resistance to 6‐thioguanine and DNA topoisomerase II poison etoposide, respectively.[3] Shalem et al.