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Mutations of the ten eleven translocation 2 gene (TET2) have recently been reported in myelodysplastic syndrome and myeloproliferative neoplasms. We analyzed the incidence and prognostic value of TET2point mutations and other genomic alterations by direct sequencing and single nucleotide polymorphism microarray analysis in 111 de novo acute myeloid leukemia, who had all achieved complete remission (CR). Mutations were observed in 19 (17%) of the 111 patients compared with 10 (27%) of 36 patients who had failed to achieve CR (P= .2). In the 111 patients who had achieved CR, TET2alterations were only significantly associated with NPM1mutations but not with other pretreatment characteristics. TET2gene status was not significantly correlated with disease-free survival and overall survival, both in the entire cohort and in patients with normal karyotype.

Familial platelet disorder (FPD), a rare autosomal dominant disorder characterized by quantitative and qualitative platelet abnormalities, is considered as a model of genetic predisposition to acute myeloid leukemia (AML). So far, monoallelic RUNX1germline mutations have been found in 19 of 20 families with reported FPD, and the analysis of blast cells from only 5 patients at acute leukemia (AL) stage has shown no additional RUNX1abnormality. Here, we performed RUNX1analysis at constitutional and somatic levels in 8 persons with FPD who developed AL from 4 independent families. In addition to the germline RUNX1mutation, we identified a second RUNX1alteration in 6 AML cases (acquired point mutations in 4 cases and duplication of the altered RUNX1allele associated with acquired trisomy 21 in 2 other cases). Although haploinsufficiency of RUNX1causes FPD, our findings suggest that a second genetic event involving RUNX1is often associated with progression to AML.

Acquired molecular abnormalities (mutations or chromosomal translocations) of the RUNX1transcription factor gene are frequent in acute myeloblastic leukemias (AMLs) and in therapy-related myelodysplastic syndromes, but rarely in acute lymphoblastic leukemias (ALLs) and chronic myelogenous leukemias (CMLs). Among 18 BCR-ABL+leukemias presenting acquired trisomy of chromosome 21, we report a high frequency (33%) of recurrent point mutations (4 in myeloid blast crisis [BC] CML and one in chronic phase CML) within the DNA-binding region of RUNX1. We did not found any mutation in de novo BCR-ABL+ALLs or lymphoid BC CML. Emergence of the RUNX1mutations was detected at diagnosis or before the acquisition of trisomy 21 during disease progression. In addition, we also report a high frequency of cryptic chromosomal RUNX1translocation to a novel recently described gene partner, PRDM16on chromosome 1p36, for 3 (21.4%) of 14 investigated patients: 2 myeloid BC CMLs and, for the first time, 1 therapy-related BCR-ABL+ALL. Two patients presented both RUNX1mutations and RUNX1-PRDM16fusion. These events are associated with a short survival and support the concept of a cooperative effect of BCR-ABLwith molecular RUNX1abnormalities on the differentiation arrest phenotype observed during progression of CML and in BCR-ABL+ALL.

Targeting the tyrosine kinase activity ofBCR-ABLrepresents a very promising therapeutic strategy in chronic myeloid leukemia (CML). Despite strong efficacy of the tyrosine kinase inhibitor STI571, resistance has been observed in a significant proportion of patients in advanced CML stage or in Ph-positive acute lymphoid leukemia (ALL). We investigated in this study the mechanism of resistance to STI571 through point mutations in the tyrosine kinase domain and/or BCR-ABLgene amplification in 24 patients (16 in chronic phase and 8 in accelerated phase of the disease) who obtained no cytogenetic response to STI571 treatment. Screening for the already-described Thr315Ile point mutation in the ABLdomain using a reverse transcription polymerase chain reaction restriction fragment length polymorphism (RT-PCR-RFLP) technique, 3 patients showed a proportion of mutated transcript at the time of resistance. The same technique failed to detect mutation at diagnosis, but a specific allele-specific oligonucleotide (ASO)–PCR on DNA for the Thr315Ile mutation and, after sequencing, for 2 newly described Phe311Leu and Met351Thr substitutions, showed the presence of rare mutated cells prior to STI571 therapy. Furthermore, the increased proportion of mutated cells during treatment detected by ASO-PCR strongly suggested clonal selection by the functional inhibiting effect of these mutations. Finally, no BCR-ABLgene amplification was detected by fluorescent in situ hybridization (FISH) in the 24 STI571-resistant patients. Our data support that in CML patients treated with STI571, ABLmutations are not restricted to the accelerated phase of the disease and that, at least in some cases, mutations seem to occur prior to STI571 therapy, probably as second mutational events during the course of CML.

The p16 protein is a cyclin inhibitor encoded by a gene located in 9p21, which may have antioncogenic properties, and is inactivated by homozygous p16 gene deletion or, less often, point mutation in several types of solid tumors often associated to cytogenetic evidence of 9p21 deletion. We looked for homozygous deletion and point mutation of the p16 gene in acute lymphoblastic leukemia (ALL), where 9p21 deletion or rearrangement are also nonrandom cytogenetic findings. Other hematologic malignancies including acute myeloid leukemia (AMD, myelodysplastic syndromes (MDS), chronic lymphocytic leukemia (CLL), and myeloma were also studied. Homozygous deletion of the p16 gene was seen in 9 of the 63 (14%) ALL analyzed, including 6/39 precursor B-ALL, 3/12 T-ALL, and 0/12 Burkitt's ALL. Three of the 7 ALL with 9p rearrangement (including 3 of the 5 patients where this rearrangement was clearly associated to 9p21 monosomy) had homozygous deletion compared to 5 of the 55 patients with normal 9p (the last patient with homozygous deletion was not successfully karyotyped). Single stranded conformation polymorphism analysis of exons 1 and 2 of the p16 gene was performed in 88 cases of ALL, including the 63 patients analyzed by Southern blot. Twenty-six of the cases had 9p rearrangement, associated to 9p21 monosomy in at least 12 cases. A missense point mutation, at codon 49 (nucleotide 164), was seen in only 1 of the 88 patients. No homozygous deletion and no point mutation of the p16 gene was seen in AML, MDS, CLL, and myeloma. Homozygous deletion of interferon α genes (situated close to p16 gene in 9p21) was seen in only 3 of the 9 ALL patients with p16 gene homozygous deletion, and none of the ALL without p16 gene homozygous deletion. Our findings suggest that homozygous deletion of the p16 gene is seen in about 15% of ALL cases, is not restricted to cases with cytogenetically detectable 9p deletion, and could have a pathogenetic role in this malignancy. On the other hand, p16 point mutations are very rare in ALL, and we found no p16 homozygous deletions or mutations in the other hematologic malignancies studied.

Mutation of the nucleophosmin (NPM) gene has been reported as the most frequent mutation in acute myeloid leukemia (AML), especially in the presence of a normal karyotype. In this subgroup of intermediate-risk AML, the identification of other gene mutations (eg, FLT3, CCAAT/enhancer-binding protein-α [CEBPA]) has helped to refine the prognosis. This study explored the prevalence and the prognostic impact of NPM mutations in a cohort of 106 patients with normal-karyotype AML. NPMexon 12 mutations were detected by polymerase chain reaction (PCR) and fragment analysis for the insertion/deletion globally resulting in a 4-bp insertion. NPM mutations were detected in 47% of patients and were associated with a high white blood cell count, involvement of the monocytic lineage (M4/M5), and a decreased prevalence of CEBPA mutations. Complete remission rate and long-term outcome did not differ between NPM-mutated and -nonmutated patients. Prospective studies are needed to confirm the definitive place of NPMmutation detection to predict AML response to therapy.

Abstract 163