Clinical Characteristics, Treatment Approach and Long-Term Outcomes of 678 Patients with Symptomatic Waldenstrom's Macroglobulinemia: Comprehensive Insights from a Spanish Registry of IgM Gammapathies

Introduction The pathogenesis of Waldenstrom's macroglobulinemia (WM) involves the clonal expansion of lymphoplasmacytic B cells in bone marrow, producing monoclonal immunoglobulin M (IgM). The heterogeneity of clinical manifestations in this uncommon disease represents the treatment approach more challenging. Multicenter registries may help in improving health care and scientific research. PRAME is a Spanish national registry of WM and IgM-related disorders with comprehensive data collection, providing insights for a better understanding of WM. Methods This is a retrospective, multicenter study that included newly diagnosed symptomatic WM (SWM) patients, evaluated at (24) Spanish hospitals between 1990 and 2023. All patients had confirmed diagnoses of SWM according to the International Workshop Consensus. Data collection on patients' demographics and disease epidemiology, clinical characteristics, diagnosis, treatment approaches and outcomes were performed from patients' local medical files. Results From 1796 total patients included in the Spanish registry for IgM gammopathies, a total of 678 newly SWM patients were identified. The median age was 71(range 35-94) years, 37% of patients had aged ≥ 75 years and 63% were male. The most common symptom at diagnosis was anemia (43%), followed by B symptoms (30%). Fifteen percent had peripheral neuropathy (PN) as the first WM symptom (39% with sensitive motor PN). Hyperviscosity was only observed in 15%. The free light chain isotypes were mostly kappa (75.4%). Less than 5% of the total cohort, had an ECOG ≥3, at diagnosis. Among 403 patients, who had samples available for assessing MYD88L265P by quantitative allele-specific PCR, 75% were positive for the mutation. However, out of the 199 patients assessed for CXCR4(S388X) mutation, only 12% were positive. The first line of therapy was started in 98% of patients. Plasmapheresis was indicated in 10%, with a median number of 2 sessions. The most frequent indications for initiating the treatment were anemia (48%), B symptoms (13%), and neuropathy (9%). Symptoms related to IgM monoclonal and extramedullary involvement were seen in 15% (56% associated with hyperviscosity) and 11.3%, respectively. The main first-line treatment regimens received were: chlorambucil (37%), dexamethasone, rituximab and cyclophosphamide (DRC)(21%), rituximab monotherapy (13%), bendamustine/rituximab (BR) (9.1%), Bruton tyrosine kinase (BTK) inhibitors (7%), and bortezomib, dexamethasone and