CBL Mutations In Therapy-Related Leukemia and Infant Leukemia

Abstract 2149

Recent reports of somatic mutations of the CBL proto-oncogene in myeloid neoplasms are intriguing, because these CBL mutations were shown to results in aberrant tyrosine kinase signaling, which would lead also to activation of RAS signaling pathways. We and others reported that CBL mutations occurred in a variety of myeloid neoplasms, including de novo acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and MDS/myeloproliferative neoplasm, especially in chronic myelomonocytic leukemia (CMML) and juvenile myelomonocytic leukemia (JMML). The importance of CBL mutations concerning leukemogenesis is substantially increased. We investigated CBL mutations in 20 therapy-related leukemia/MDS (t-Leuk/MDS) cases and 26 infant leukemia cases. Homozygous mutation of theCBL gene (P417R), which was located in the RING finger domain, was identified in one out of 20 (5%) t-Leuk/MDS cases. This patient was a 5 year-old boy, whose biopsied specimen of the buccal lymph node showed malignant lymphoma (diffuse large T cell type, MT1(+), MB1(-), UCHL1(+)). No pathogenic nucleotide changes were identified in the CBL gene in the initial sample. Subsequently, the patient was treated with chemotherapy including VP-16 (200 mg/m²) given twice weekly. Nineteen months after initial diagnosis, he was diagnosed as having therapy-related leukemia with t(5;21) and MLL gene rearrangement due to VP-16. Furthermore, CBL gene mutations were found in 3 of 26 (12%) infant leukemia cases with 11q23 translocation/MLL gene rearrangement. CBL gene mutations were located in splice site in intron 8 and the RING finger domain (Y371H, in 2 cases), SNP array analysis (Affymetrix, GeneChip) of these cases with mutated CBL gene disclosed 11q-acquired uniparental disomy in all cases, but not in cases with wild-type CBL. CBL mutation has not been reported in acute leukemia with 11q23 translocation/MLL gene rearrangement. To our knowledge, these are the first t-Leuk/MDS case and infant cases with 11q23 translocation/MLL rearrangement, suggesting that CBL is mutated in a unique subset of t-Leuk/MDS and infant leukemia which is considered to play a pathogenic role in the development of t-Leuk/MDS and infant leukemia. Further accumulation of cases with t-Leuk/MDS and infant leukemia having the CBL mutation is needed.