Beyond BCR::ABL1—The Role of Genomic Analyses in the Management of CML

Abstract

Chronic myeloid leukemia (CML) is a model of genomically based diagnosis and management where BCR::ABL1 is successfully targeted by tyrosine kinase inhibitor (TKI) therapy in most patients. The dynamics of BCR::ABL1 transcript decline during therapy is a dependable biomarker of response, relapse, and drug resistance. Missense mutations acquired within the BCR::ABL1 kinase domain that disrupt TKI binding can evolve during therapy and are frequently detected in patients for whom TKI treatment fails. Importantly, specific BCR::ABL1 missense mutations are targetable alterations and direct therapeutic decisions based on the individual mutant TKI sensitivity profile. Nevertheless, BCR::ABL1 mutations are only implicated in approximately half of the cases of acquired resistance. Furthermore, not all patients with a single BCR::ABL1 mutation that is predicted to be sensitive to a specific TKI will experience a response when switched to that TKI. Progression to blast phase heralds independence from BCR::ABL1, and this phase of the disease is notoriously difficult to treat. The independent drivers of resistance and disease progression have long been investigated to both predict progression and to find targets for therapeutic intervention. Recent data reaffirm that drug resistance and disease progression is a mutation-driven process in CML, and somatic variants in genes that are known to drive acute myeloid and lymphoid leukemia have been detected in patients in the advanced phases of CML. Genomic testing over the last few decades for patients with blood cancer has revealed of variety of genomic aberrations that drive disease. Consequently, incorporation of genomic factors into patient management for a range of blood cancers has led to the implementation of high-throughput gene testing to detect clinically actionable variants. Is it time to integrate broader genomic screening into clinical management strategies for patients with CML?