Biallelic TET2 mutation sensitizes to 5-azacitidine in acute myeloid leukemia

Precision medicine can significantly improve outcomes for cancer patients, but implementation requires comprehensive characterization of tumor cells to identify therapeutically exploitable vulnerabilities. Here we describe somatic biallelic TET2 mutation (focal deletion and nonsense mutation) in an elderly patient with acute myeloid leukemia (AML) that was chemoresistant to anthracycline and cytarabine, but acutely sensitive to 5-azacitidine (5-Aza) hypomethylating monotherapy, resulting in long-term morphological remission (overall survival (OS) 850 days). Given the role of TET2 as a regulator of genomic methylation, we hypothesized that mutant TET2 allele dosage affects response to 5-Aza. Using an isogenic cell model system and an orthotopic mouse xenograft, we demonstrate that biallelic TET2 mutations confer sensitivity to 5-Aza compared to cells with monoallelic mutation. We subsequently identified 29 additional patients from the Study Alliance Leukemia biobank with chromosome 4 abnormalities and identified two further patients with complex biallelic TET2 mutations, including one with trisomy 4, homozygosity across the long arm and an inactivating point mutation. We also screened patients recruited to the PETHEMA FLUGAZA phase 3 clinical trial and identified three patients with biallelic TET2 mutations, two of whom had responded very well to single agent 5-Aza (OS 767 and 579 days) despite having adverse risk AML and poor performance status. Our data argue in favor of using hypomethylating agents for chemoresistant disease or as first line therapy in patients with biallelic TET2-mutated AML and demonstrate the importance of considering mutant allele dosage in the implementation of precision medicine for cancer patients. Key PointsO_LIMutant TET2 allele dosage affects response to 5-azacitidine in acute myeloid leukemia in vitro and in a xenograft model. C_LIO_LIOur data highlight the importance for screening of biallelic mutations to predict response to therapy in acute myeloid leukemia. C_LI