Upon further analysis, which included bone marrow biopsy, flow cytometry, immunohistochemistry, fluorescence in situ hybridization, and MYD88 (L265P) gene mutation analysis, the rare diagnosis of IgM multiple myeloma was confirmed.
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 × 10(-5) for WM vs other cohorts).
Although not entirely specific, MYD88 L265P is a useful adjunct for bone marrow diagnosis in separating LPL from other small B-cell lymphomas and plasma cell myeloma.
MYD88 L265P was absent in paired normal tissue samples from patients with Waldenström's macroglobulinemia or non-IgM LPL and in B cells from healthy donors and was absent or rarely expressed in samples from patients with multiple myeloma, marginal-zone lymphoma, or IgM monoclonal gammopathy of unknown significance.