Key Points• The MYD88 locus is altered in 91% of patients with WM. • MYD88 might be new target for therapeutic in WM.Mutation of the MYD88 gene has recently been identified in activated B-cell-like diffuse cell lymphoma and enhanced Janus kinase/signal transducer and activator of transcription (JAK-STAT) and nuclear factor kB (NF-kB) signaling pathways. A whole exome-sequencing study of Waldenstrom macroglobulinemia (WM) suggested a high frequency of MYD88 L265P mutation in WM. The genetic background is not fully deciphered in WM, although the role of NF-kB and JAK-STAT has been demonstrated. We analyzed MYD88 mutation in exon 5 and characterized the clinical significance of this genetic alteration in 67 WM patients. Clinical features; immunophenotypic markers; and conventional cytogenetic, fluorescence in situ hybridization, and single nucleotide polymorphism array data were analyzed. MYD88 L265P mutation was acquired in 79% of patients. Overall, we have identified alteration of the MYD88 locus in 91% of WM patients, including 12% with gain on chromosome 3 at the 3p22 locus that included the MYD88 gene. Patients with absence of MYD88 mutation were WM characterized with a female predominance, a splenomegaly, gain of chromosome 3, and CD27 expression. Importantly, inhibition of MYD88 signaling induced cytotoxicity and inhibited cell growth of cell lines issued from patients with WM. In conclusion, these results confirm a high frequency of MYD88 L265P mutation in WM. The discovery of MYD88 L265P mutation may contribute to a better understanding of the physiopathogeny of WM. (Blood. 2013;121(22):4504-4511)

To address these issues, we conducted a cytogenetic study of a large series of untreated symptomatic patients enrolled in a prospective, randomized, open-label clinical trial. The WM1 study took place in 101 centers in five countries and enrolled 339 patients with WM, 37 patients with non-MALT marginal zone lymphoma (MZL), and 38 patients with lymphoplasmacytic lymphoma, who were all randomly assigned to receive chlorambucil or fludarabine. 7Here we report our cytogenetic findings in 174 of the WM patients enrolled in this trial.

Purpose: Whole-genome sequencing has revealed MYD88 L265P and CXCR4 mutations (CXCR4 mut ) as the most prevalent somatic mutations in Waldenstr€ om macroglobulinemia. CXCR4 mutation has proved to be of critical importance in Waldenstr€ om macroglobulinemia, in part due to its role as a mechanism of resistance to several agents. We have therefore sought to unravel the different aspects of CXCR4 mutations in Waldenstr€ om macroglobulinemia.Experimental Design: We have scanned the two coding exons of CXCR4 in Waldenstr€ om macroglobulinemia using deep nextgeneration sequencing and Sanger sequencing in 98 patients with Waldenstr€ om macroglobulinemia and correlated with SNP array landscape and mutational spectrum of eight candidate genes involved in TLR, RAS, and BCR pathway in an integrative study.Results: We found all mutations to be heterozygous, somatic, and located in the C-terminal domain of CXCR4 in 25% of the Waldenstr€ om macroglobulinemia. CXCR4 mutations led to a truncated receptor protein associated with a higher expression of CXCR4. CXCR4 mutations pertain to the same clone as to MYD88 L265P mutations but were mutually exclusive to CD79A/CD79B mutations (BCR pathway). We identified a genomic signature in CXCR4 mut Waldenstr€ om macroglobulinemia traducing a more complex genome. CXCR4 mutations were also associated with gain of chromosome 4, gain of Xq, and deletion 6q.Conclusions: Our study panned out new CXCR4 mutations in Waldenstr€ om macroglobulinemia and identified a specific signature associated to CXCR4 mut , characterized with complex genomic aberrations among MYD88L265P Waldenstr€ om macroglobulinemia. Our results suggest the existence of various genomic subgroups in Waldenstr€ om macroglobulinemia.

We recently isolated the RhoH/TTF gene by its fusion to the LAZ3/BCL6 gene, in a non-Hodgkin's lymphoma (NHL) cell line, which bore a t(3;4)(q27;p11 ± 13) translocation. This gene encodes a novel Rho GTP-binding protein and is speci®cally expressed in hematopoietic tissues. We made its precise mapping at band 4p13, and described its partial genomic structure. Using¯uorescence in situ hybridization and molecular analyses, we report here on the rearrangement of the RhoH/TTF gene, at band 4p13, in four cases of NHL with t(3;4)(q27;p13) translocation and its fusion to the LAZ3/BCL6 gene at band 3q27, in three of these cases. RT ± PCR analysis of two cases allowed the detection of variable fusion transcripts emerging from the rearranged alleles, and in one case, a deregulated expression of both RhoH/TTF and LAZ3/BCL6 genes, by promoter substitution, was observed. We also show here another rearrangement of the RhoH/TTF gene in a patient with multiple myeloma and t(4;14)(p13;q32) translocation, with breakage within the IGH gene. It is the ®rst report which describes the recurrent chromosomal alteration of a GTP-binding protein encoding gene, in patients with hematopoietic malignancies.

SNP array (SNPa) was developed to detect copy number alteration (CNA) and loss of heterozygosity (LOH) without copy number changes, CN-LOH. We aimed to identify novel genomic aberrations using SNPa in 31 WM with paired samples. Methylation status and mutation were analyzed on target genes. A total of 61 genetic aberrations were observed, 58 CNA (33 gains, 25 losses) in 58% of patients and CN-LOH in 6% of patients. The CNA were widely distributed throughout the genome, including 12 recurrent regions and identified new cryptic clonal chromosomal lesions that were mapped. Gene set expression analysis demonstrated a relationship between either deletion 6q or gain of chromosome 4 and alteration of gene expression profiling. We then studied methylation status and sought for mutations in altered regions on target genes. We observed methylation of DLEU7 on chromosome 13 in all patients (n 5 12) with WM, and mutations of CD79B/CD79A genes (17q region), a key component of the BCR pathway, in 15% of cases. Most importantly, higher frequency of 3 CNA was observed in symptomatic WM. In conclusion, this study expands the view of the genomic complexity of WM, especially in symptomatic WM, including a potentially new mechanism of gene dysfunction, acquired uniparental disomy/CN-LOH. Finally, we have identified new potential target genes in WM, such as DLEU7 and CD79A/B. Am. J.