MYD88 L265P is a commonly recurring mutation in patients with Waldenström's macroglobulinemia that can be useful in differentiating Waldenström's macroglobulinemia and non-IgM LPL from B-cell disorders that have some of the same features. (Funded by the Peter and Helen Bing Foundation and others.).

Ibrutinib was highly active, associated with durable responses, and safe in pretreated patients with Waldenström's macroglobulinemia. MYD88 and CXCR4 mutation status affected responses to this drug. (Funded by Pharmacyclics and others; ClinicalTrials.gov number, NCT01614821.).

Key Points Highly recurring mutations are present in WM, including MYD88 L265P, warts, hypogammaglobulinemia, infection, and myelokathexis-syndrome–like mutations in CXCR4, and ARID1A. Small, previously undetected CNAs affecting B-cell regulatory genes are highly prevalent in WM.

Key Points• MYD88 L265P is expressed in WM and IgM MGUS patients using AS-PCR assays with potential use in diagnostic discrimination and response assessment.By whole-genome and/or Sanger sequencing, we recently identified a somatic mutation (MYD88 L265P) that stimulates nuclear factor kB activity and is present in >90% of Waldenström macroglobulinemia (WM) patients. MYD88 L265P was absent in 90% of immunoglobulin M (IgM) monoclonal gammopathy of undetermined significance (MGUS) patients. We therefore developed conventional and real-time allele-specific polymerase chain reaction (AS-PCR) assays for more sensitive detection and quantification of MYD88 L265P. Using either assay, MYD88 L265P was detected in 97 of 104 (93%) WM and 13 of 24 (54%) IgM MGUS patients and was either absent or rarely expressed in samples from splenic marginal zone lymphoma (2/20; 10%), CLL (1/26; 4%), multiple myeloma (including IgM cases, 0/14), and immunoglobulin G MGUS (0/9) patients as well as healthy donors (0/40; P < 1.5 3 10 25 for WM vs other cohorts). Real-time AS-PCR identified IgM MGUS patients progressing to WM and showed a high rate of concordance between MYD88 L265P DC T and BM disease involvement (r 5 0.89, P 5 .008) in WM patients undergoing treatment. These studies identify MYD88 L265P as a widely present mutation in WM and IgM MGUS patients using highly sensitive and specific AS-PCR assays with potential use in diagnostic discrimination and/or response assessment. The finding of this mutation in many IgM MGUS patients suggests that MYD88 L265P may be an early

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MYD88 L265P is highly prevalent in Waldenstrom's Macroglobulinemia (WM) and IgM monoclonal gammopathy of unknown significance (MGUS). We investigated whether MYD88 L265P could be identified by peripheral blood (PB) allele-specific PCR. MYD88 L265P was detected in untreated WM (114/118; 96.6%); previously treated WM (63/102; 61.8%); and IgM MGUS (5/12; 41.7%) but in none of 3 hyper-IgM or 40 healthy individuals. Median PB MYD88 L265P ΔCt was 3.77, 7.24, 10.89, 12.33 and 14.07 for untreated WM, previously treated WM, IgM MGUS, hyper-IgM and healthy individuals, respectively (P<0.0001). For the 232 IgM MGUS and WM patients, PB MYD88 L265P ΔCt moderately correlated to bone marrow (BM) disease (r=-0.3553; P<0.0001), serum IgM (r=-0.3262; P<0.0001) and hemoglobin (r=0.3005; P<0.0001) levels. PB MYD88 L265P ΔCt and serum IgM correlated similarly with BM disease burden. For positive patients, PB MYD88 L265P ΔCt was <6.5 in 100/114 (88%) untreated WM, and >6.5 in 4/5 (80%) IgM MGUS patients (P=0.0034). Attainment of a negative PB MYD88 L265P mutation status was associated with lower BM disease (P=0.001), serum IgM (P=0.019) and higher hemoglobin (P=0.004) levels in treated patients. These studies show the feasibility for detecting MYD88 L265P by PB examination, and the potential for PB MYD88 L265P ΔCt use in the diagnosis and management of WM patients.

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Waldenström's macroglobulinemia (WM) is characterized by bone marrow (BM) infiltration with lymphoplasmacytic cells and production of an IgM paraprotein. Lymphocytosis is uncommon in WM, and many patients exhibit peripheral B-cell lymphopenia. Recently, by whole genome sequencing, we identified a highly recurrent somatic mutation (L265P) in MYD88. Using real-time allele-specific polymerase chain reaction (AS-PCR), we demonstrated the presence of MYD88 L265P in 93% and 54% of patients with WM and IgM monoclonal gammopathy of undetermined significance (MGUS), respectively (Xu et al, Blood 2013). To clarify the feasibility of using real-time AS-PCR assay to detect MYD88 L265P in peripheral blood, we first examined unselected mononuclear cells from peripheral blood (PB) samples of 88 patients with untreated WM. 81/88 (92%) of these patients were MYD88 L265P positive by bone marrow (BM) examination of CD19 selected B-cells; Of the 81 BM-MYD88 L265P positive patients, 32 (40%) demonstrated MYD88 L265P by AS-PCR in unselected PB mononuclear cells (PBMC) obtained at the time of BM examination. To enhance the ability to detect MYD88 L265P in PB samples, we next used AS-PCR in CD19 selected PBMC obtained from 198 WM patients which included untreated and previously treated patients. Among untreated patients, 106/118 (89.8%) were positive for MYD88 L265P in CD19 selected PB, whereas among previously treated patients, 55/80 (68.8%) were positive for MYD88 L265P (p=0.0002 vs. untreated). Simultaneously analyzed PB and BM samples from 65 untreated WM patients demonstrated positivity for MYD88 L265P in 58/65 (89.2%) and 55/65 (84.6%) of CD19 selected BM and PB samples, respectively. These findings yielded a sensitivity of 94.8%, specificity of 100%, positive and negative predictive values of 100% and 70%, respectively for AS-PCR testing of PB CD19+ cells for MYD88 L265P in untreated WM patients. In addition, we analyzed 12 untreated IgM MGUS patients with paired sampling of CD19 selected PB and BM cells. 6/12 (50%) IgM MGUS patients were positive for MYD88 L265P in BM CD19+ cells, with 5/6 (83%) of these positive patients demonstrating MYD88 L265P by AS-PCR in CD19 selected PB samples. The overall results demonstrate a high concordance of MYD88 L265P status between PB and BM CD19 selected samples, particularly in untreated WM patients. The detection of MYD88 L265P by CD19 selected PB AS-PCR examination provides a convenient and less invasive method to support the diagnosis of WM and IgM MGUS. Disclosures: No relevant conflicts of interest to declare.