Spliceosome GENE MUTATIONS ARE Also PRESENT In the Diverse Mutational Spectrum of CHRONIC Myelomonocytic LEUKEMIA

Abstract 1402

Chronic myelomonocytic leukemia (CMML) is characterized by monocytic proliferation, cytomorphologic dysplasia and frequent progression to acute myelogeneous leukemia (AML). The molecular basis of CMML is poorly defined, although somatic mutations in a number of genes have recently been identified in a proportion of patients (epigenetic regulatory genes, spliceosomal genes, apoptosis genes, growth signal transducers and others). We performed a comprehensive analysis of molecular lesions, including somatic mutations detected by sequencing and chromosomal abnormalities investigated by metaphase and SNP-array karyotyping. We have selected a cohort of 72 patients (36 CMML1, 16 CMML2 and 20 sAML evolved from CMML).

Our mutational screen performed in stages (as new mutations were discovered by our and other groups) and currently reveals mutations in UTX in 8%, DNMT3A in 9%, CBL in 14%, IDH1/2 in 4%, KRAS in 2.7%, NRAS in 4.1%, JAK2 in 1%, TET2 in 48%, ASXL1 in 43%, EZH2 in 5.5%, RUNX1 37%. Based on the discovery of various spliceosomal mutations in myeloid malignancies, novel mutations were also found in CMML, in U2AF1 in 12%, SF3B1 in 14%, SFRS19 in 6 % of cases tested.

Chromosomal defects were detected in 60% of patients. In particular, a high frequency of somatic uniparental disomy (sUPD) were identified 71% of patients with abnormal cytogenetics, including UPD1p (N=3), UPD7q (N=8), UPD4q (N=6), UPD2p (N=2), UPD17q (N=2), UPD11q (N=5), UPDX (N=1), UPD21q (N=2). Some of the detected mutations were homozygous through their association with sUPD as for example for 3 EZH2, 1 UTX, 6 TET2, 2 DNMT3A, 5 CBL, 1 NRAS, 1 U2AF1 mutations. Furthermore, UPD17p implies that a P53 mutation is also present in this case as previously LOH17p was shown to be invariably associated with P53 mutations. Similarly, 2 cases of UPD17q imply that homozygous mutation of SRSF2, which is one of the Serine/arginine-rich splicing factor, may be present in this location and the mutation analysis is ongoing.

In over 90% of >1 mutation was found but many patients harbored multiple mutations with frequent combinations of TET2/CBL or TET2/ASXL1 as well as RUNX1 and U2AF1 serving as examples. There was an accumulation of mutations from sAML, CMML2 and CMML1 suggesting stepwise accumulation of lesions. In serial studies, some of the mutations were present at the inception (e.g., TET2, ASXL1 and DNMT3A) in some cases originally heterozygous mutations were also while other can occur in the course of disease (e.g. CBL). RAS and DNMT3A mutations were associated with a higher blasts count.

In sum, combined analysis of molecular lesions in CMML reveals that similar phenotype may be a result of diverse mutations associated with seemingly unrelated pathways and that clinical phenotype may be a result of a combination of mutations which accumulate as the disease progresses. Survival analyses will require large cohorts to account for various confounding factors including the presence of multiple chromosomal abnormalities and mutations in one patient, however currently EZH2, DNMT3 and CBL mutations appear to convey less favorable prognosis.