MYD88 Negative Waldenstrom Macroglobulinemia Has Distinct Clinical & Biological Features As Compared To Its MYD88 Mutant Counterpart

Waldenstrom Macroglobulinemia (WM) harbors a mutation in MYD88 gene (MYD88L265P) with frequencies varying from 67% to 91%. Although of diagnostic use its clinical significance in terms of prognosis and treatment response is unclear. We retrospectively analyzed WM for MYD88 L265P mutation, immunogenetic profile (presence of somatic hypermutations and biased gene usage) & correlated these with standard clinical variables including prognosis and patient outcome.

32 cases WM (diagnosed as per WHO 2008/2001 criteria) were retrospectively accrued from 2007-2013. Genomic DNA extracted from bone marrow aspirate smears was subjected to an allele specific oligonucleotide PCR to detect the MYD88L265P mutation using fluorescently labeled primers followed by capillary electrophoresis. Immunogenetics was assessed in 29 patients. Clonal FR1/FR2 regions of the VH gene were amplified & sequenced. Sequence data was compared to the closest germline sequences on NCBI & IMGT databases. Laboratory variables (Hb, WBC, platelet, M Protein concentration, S. IgM, b2M level, S. Globulin, LDH, %of lymphoplasmacytic lymphocytes) were evaluated at baseline along with the International Prognostic Index (ISSWM). Response evaluation was done as per VIth International Consensus guidelines after treatment as well as at last follow up. 2-tailed Student's t-Test & Chi squared test were applied for statistical analysis.

Median age was 60 years (range: 46-77), male predominant (87.5%).Majority of patients had cytopenia (90.6%) of one or more blood lineages. Median IWSSM was 3 (n=26). The median follow up was 21.5 months (range: 1 week to 82 months). Majority of patients were treated with cyclophosphamide/vincristine/prednisone ± rituximab (55.1%), followed in others by bendamustine/rituximab(13.8%) or fludarabine/cyclophosphamide/rituximab,(13.8%) or cyclophosphamide/thalidomide/dexamethasone (10.3%). MYD88 L265P mutation was found in 84.3% (27/32) of patients. The immunogenetic results here pertain only to samples with productive IGHV gene rearrangement [22/29 (∼76%) cases]. 96% of cases revealed somatic hypermutations. 59% of cases showed a biased use for the VH3 gene followed by VH4 (22.7%) and VH1 (18.18%). The commonest gene used was IGHV3-7 (27.3%) followed by IGHV1-18 (18.2%). Clinical features separating MYD88 negative from MYD88 mutated WM are seen in Table 1. MYD88 negative WM presented with lower number of infiltrating tumor cells in the bone marrow (p=0.05), older age (p=0.02) and had a lower IWSSM score at presentation (p=0.03) as compared to mutated WM. Majority of the MYD88 negative group were in VGPR,(very good partial response) or CR (complete response) (75%:VGPR/CR) post treatment as compared to MYD88 mutated patients [21%: VGPR/CR, 31.6%: PR (partial response): 26.3%, SD (stable disease):15.8%, PD (progressive disease):6.3%]. At the last follow up 44.4% of MYD88 mutated WM had PD where as no patient in MYD88 WT had changed their initial post treatment status. Two patients with MYD88 mutation died due to disease related complications.

Our data indicates that WM is a biologically heterogeneous subset dichotomized by MYD88 mutations. WM patients with MYD88 mutations present at younger age with high tumor burden in the bone marrow, high risk of progression and poor therapeutic response. Although limited in number, MYD88 negative WM patients were not associated with PD as compared to the mutated group. Overall MYD88mutation may be considered as an adverse prognostic factor in WM.

No relevant conflicts of interest to declare.