Retrospective-prospective Study to Evaluate Treatment Management and Outcomes of Patients With Waldenström's Macroglobulinemia (WM) Treated in Italy According to the Zanubrutinib (Brukinsa®) Compassionate Use Program (CUP) and in Common Practice Following Commercial Approval.

Inclusion Criteria: * Signed and dated informed consent form * Waldenström's macroglobulinemia diagnosis in need of treatment according to ESMO (European Society for Medical Oncology) guideline 2018 * Patients who received Zanubrutinib according to the Italian CUP or in common practice following Zanubrutinib commercial approval * Treatment with zanubrutinib according to current SmPC (Summary of Product Characteristics) * Treatment decision before inclusion into this non-interventional study * Age ≥18 years Exclusion Criteria: * Contraindications according to SmPC for patients with WM * Participation in an interventional clinical trial during zanubrutinib treatment * Patients with disease progression during a BTKi treatment (if pre-treated with BTK, only those intolerants are considered eligible)