Recently, we and other groups reported in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) a strong correlation between cytogenetic rearrangements leading to 17p deletion, a typical form of dysgranulopoiesis combining pseudo-Pelger-Huët hypolobulation and small vacuoles in neutrophils, and p53 mutation. To gain further insight into this “17p-syndrome,” we studied 17 cases of AML and MDS with 17p deletion by whole chromosome painting (WCP) and fluorescence in situ hybridization (FISH) with probes spanning the 17p arm, including a p53 gene probe. Cytogenetically, 15 patients had unbalanced translocation between chromosome 17 and another chromosome (chromosome 5 in nine cases and unidentified chromosome -add 17p- in three cases), one patient had monosomy 17, and one had i(17q). All rearrangements appeared to result in 17p deletion. Sixteen patients had additional cytogenetic rearrangements. WCP analysis confirmed the cytogenetic interpretation in all cases and identified one of the cases of add 17p as a t(17;22). WCP also identified chromosome 17 material on a marker or ring chromosome in two cases of t(5;17). FISH analysis with 17p markers made in 16 cases showed no deletion of the 17p markers studied in the last two patients, who had no typical dysgranulopoiesis; p53 mutation analysis in one of them was negative. In the 14 other cases, FISH showed a 17p deletion of variable extent but that always included deletion of the p53 gene. All 14 patients had typical dysgranulopoiesis, and all but one had p53 mutation and/or overexpression. These findings reinforce the morphologic, cytogenetic, and molecular correlation found in the 17p- syndrome and suggest a pathogenetic role for inactivation of tumor suppressor gene(s) located in 17p, especially the p53 gene.

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Recently, we and other groups reported in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) a strong correlation between cytogenetic rearrangements leading to 17p deletion, a typical form of dysgranulopoiesis combining pseudo-Pelger-Huët hypolobulation and small vacuoles in neutrophils, and p53 mutation. To gain further insight into this “17p-syndrome,” we studied 17 cases of AML and MDS with 17p deletion by whole chromosome painting (WCP) and fluorescence in situ hybridization (FISH) with probes spanning the 17p arm, including a p53 gene probe. Cytogenetically, 15 patients had unbalanced translocation between chromosome 17 and another chromosome (chromosome 5 in nine cases and unidentified chromosome -add 17p- in three cases), one patient had monosomy 17, and one had i(17q). All rearrangements appeared to result in 17p deletion. Sixteen patients had additional cytogenetic rearrangements. WCP analysis confirmed the cytogenetic interpretation in all cases and identified one of the cases of add 17p as a t(17;22). WCP also identified chromosome 17 material on a marker or ring chromosome in two cases of t(5;17). FISH analysis with 17p markers made in 16 cases showed no deletion of the 17p markers studied in the last two patients, who had no typical dysgranulopoiesis; p53 mutation analysis in one of them was negative. In the 14 other cases, FISH showed a 17p deletion of variable extent but that always included deletion of the p53 gene. All 14 patients had typical dysgranulopoiesis, and all but one had p53 mutation and/or overexpression. These findings reinforce the morphologic, cytogenetic, and molecular correlation found in the 17p- syndrome and suggest a pathogenetic role for inactivation of tumor suppressor gene(s) located in 17p, especially the p53 gene.

1307 Background. Mutation of MYD88 gene has recently been identified in activated B-cell like diffuse B-cell lymphoma, and enhanced JAK STAT and NF-kB signalling pathways. Whole exome sequencing study in Waldenstrom macroglobulinemia (WM) suggested a high frequency of MYD88 L265P mutation in WM. Although the genetic background is not fully deciphered in WM, the role of NF-kB and JAK STAT pathways has been demonstrated in WM; which underlying mechanisms of deregulation remain to be elucidated. We aimed to analyze MYD88 mutation in exon 5 and to characterize the clinical significance of this genetic alteration in 67 WM. Method. 67 patients (42 males, 25 females) diagnosed with WM were included in this study, along with 9 patients with chronic lymphocytic leukemia (CLL), 4 multiple myeloma (MM) and 9 marginal zone lymphoma (MZL) were also studied. Patients were untreated at time of BM collection and gave informed consent prior to research sampling. Clinical features, immunophenotypic markers using flow cytometry (Matutes score panel, CD38, CD138, CD27, CD80), conventional cytogenetic, FISH and SNP array data (n = 46) were analysed. B cells from bone marrow and T cells from blood were isolated respectively using B cell isolation kit and Pan T isolation kit (Myltenyi Biotech). For DNA sequencing of exon 5 of MYD88, the exon 5 of MYD88 gene was amplified from genomic DNA by PCR. The purified PCR products were directly sequenced in both directions using BigDye® Terminator Cycle Sequencing Kit (Applied Biosystems, CA, USA) and analyzed on the Applied Biosystems 3130xl Genetic Analyzer. Data were analyzed with SeqScape software version 2.5 (Applied Biosystems). Results. MYD88 L265P mutation (MYDmut) was observed in 79% of patients, including homozygous mutation in two patients (3%). MYD88 mutation was not identified in T lymphocytes isolated from 4 WM patients that confirmed MYD88 mutation was acquired in the tumoral cells. We haven't observed any other mutation on exon 5. We then sought for other mechanisms of MYD88 gene alteration, such as copy number alteration (CNA) and copy neutral –loss of heterozygosity (CN-LOH) also considered as an acquired UPD (uniparental disomy) at MYD88 locus. We found an UPD at MYD88 locus in solely one patient (2%), and haven't identified any deletion at 3p22. On the contrary, we observed a gain on chromosome 3 at 3p22 locus (including MYD88 gene) in 7/57 (12%) patients. Taking together, we identified alteration of the MYD88 locus in 85% of patients with WM, by either gain-of-function mutation (79%) or CNA (12%). Interestingly, we found gain on chromosome 3 more frequently in the MYDwildgroup than in the MYDmutgroup (p=0.02). Twenty one percent of the patients with WM had no mutation of MYD (MYDwild), and were characterized with a female predominance, a splenomegaly, gain of chromosome 3 and CD27 expression. We did not observed difference in terms of survival according to the MYD88 mutation status. MYD88 mutation was not related to deletion 6q, gain of 4, deletion 11q, deletion 17p, deletion 13q14 in our study. Interestingly, deletion 7q, a frequent cytogenetic aberration in marginal zone lymphoma, was rare in our series (4/57; 7%) and was independent of MYD88 mutation status (2 in the MYDwild and 2 in the MYDmut) (p=ns). No MYD88 L265P mutation was observed in CLL and MM. In MZL, 1/9 patient without M monoclonal component had a MYDL265p mutation. Conclusion. These results confirm a high frequency of MYD88 L265P mutation in WM that may become a useful biomarker for diagnostic in WM and may help better understand the physiopathogeny of WM. Disclosures: No relevant conflicts of interest to declare.