Waldenström's Macroglobulinemia

IgM-secreting lymphoplasmacytic lymphoma — MYD88 L265P mutation, hyperviscosity syndrome, and BTK inhibitor-based therapy

Key Points

• Waldenström's macroglobulinemia (WM) is a rare indolent B-cell lymphoma (lymphoplasmacytic lymphoma, LPL) defined by bone marrow LPL infiltration and serum IgM monoclonal protein.
• MYD88 L265P mutation is present in >90% of WM and activates NF-κB signaling; CXCR4 mutations (~30–40%) are associated with ibrutinib resistance and symptomatic disease.
• Hyperviscosity syndrome — headache, visual changes, confusion, and bleeding from elevated serum viscosity due to pentameric IgM — is a medical emergency requiring urgent plasmapheresis.
• Ibrutinib is the first FDA-approved agent specifically for WM and is highly effective regardless of MYD88 mutation status; zanubrutinib (ASPEN trial) has a superior tolerability profile.
• Zanubrutinib showed superiority over ibrutinib for major response rate in ASPEN trial and is now preferred for WM requiring treatment.
• Rituximab monotherapy or BR (bendamustine + rituximab) remain effective chemoimmunotherapy options, particularly for patients who prefer finite-duration therapy.
• WM is incurable but indolent; median overall survival exceeds 10 years with modern therapy, and many patients require only watchful waiting at diagnosis.

Epidemiology & Pathobiology

Waldenström's macroglobulinemia is a rare B-cell malignancy, with approximately 1,500–3,000 new cases diagnosed annually in the United States. It represents ~1–2% of all hematologic malignancies. The median age at diagnosis is ~70 years; WM is exceedingly rare before age 40. There is a slight male predominance and increased incidence in White Americans compared to Black Americans. WM is classified as lymphoplasmacytic lymphoma (LPL) infiltrating the bone marrow, lymph nodes, and spleen, with secretion of a monoclonal IgM protein. The tumor cells are clonal B cells with plasmacytic…

Clinical Presentation

WM has a diverse clinical presentation driven by two mechanisms: (1) direct tumor infiltration of marrow, lymph nodes, and spleen, and (2) the pathologic effects of the IgM paraprotein. Symptoms from bone marrow infiltration: • Anemia (most common): Normocytic, normochromic; ~40–50% of patients at diagnosis; from marrow replacement by LPL cells; accounts for most fatigue and constitutional symptoms • Lymphadenopathy and splenomegaly (~15–30%) • B symptoms: Fever, night sweats, weight loss • Fatigue and weakness IgM-mediated complications (distinctive to WM): Hyperviscosity syndrome (~15–30%…

Diagnosis & Indications for Treatment

Diagnosis (IWWM criteria): • IgM monoclonal protein of any concentration in serum • ≥10% bone marrow infiltration by lymphoplasmacytic lymphocytes (small lymphocytes, lymphoplasmacytic cells, plasma cells) on trephine biopsy • MYD88 L265P mutation (highly supportive; present in >90% of WM) • Immunophenotype: CD19+, CD20+, CD5−/+, CD10−, CD23−/+, FMC7+, surface IgM+ • CXCR4 mutation testing (guides treatment choice) Distinction from IgM MGUS: <10% BM involvement + no disease-related symptoms/signs (IgM MGUS progresses to WM/LPL at ~1.5%/year) Watch-and-wait is appropriate for asymptomatic WM…

Treatment

BTK inhibitors — preferred first-line therapy for most patients: • Ibrutinib (420 mg daily): FDA approved 2015 for WM; first targeted therapy for WM. INNOVATE trial: Superior PFS vs. rituximab monotherapy (pooled median PFS ~48 months). Active in MYD88 L265P-mutated and wildtype WM. Key toxicities: atrial fibrillation (10–16%), bleeding (avoid with anticoagulation), hypertension, arthralgias. Ibrutinib + rituximab (INNOVATE trial) superior to placebo + rituximab. • Zanubrutinib (160 mg BID or 320 mg daily): More selective BTK inhibitor; FDA approved 2021 for WM. ASPEN trial: Zanubrutinib vs.…