Smouldering Waldenström macroglobulinaemia (SMW), also known as asymptomatic/indolent WM, is clinically-defined as WM (serum monoclonal IgM≥ 30 g/l and/or≥ 10% bone marrow lymphoplasmacytic infiltration) without end-organ damage (anaemia, constitutional symptoms, hyperviscosity, lymphadenopathy or hepatosplenomegaly). The diagnosis of SWM is often incidental; active surveillance is recommended and treatment is not indicated (Kapoor et al, 2017). The International Classification of Diseases (ICD) does not recognize SWM as a separate entity. Thus, studies of WM do not account for SWM, which may influence their results. Also, epidemiological studies are difficult to perform and the actual prevalence of SWM in the United States of America (USA) is not known. The National Cancer Database (NCDB) is a joint program between the Commission on Cancer (CoC) and American Cancer Society, receiving oncology outcomes from> 1500 CoC-accredited hospitals and capturing~ 70% of all newlydiagnosed cancer cases. It is the largest public cancer database in the USA that includes patient characteristics, tumour histology, type and timing of the first-line treatment. An annual 90% follow-up-rate is required and survival outcomes are released after at least 5 years of follow-up (Boffa et al, 2017). Using the 2004–2012 database, we identified 10539 adult cases of WM by the ICD-O histology codes 9761 (WM) and 9671 (lymphoplasmacytic lymphoma). After excluding cases with inadequate follow-up (N= 1147) or different reporting/treating facility (N= 1080), 8302 cases of WM were included in this study. We used the time-to-initial-treatment or reasons for not receiving treatment to create an algorithm (Fig 1) to categorize WM by disease status: smouldering, active or unknown (Ravindran et al, 2016). Patients who were recommended to receive treatment (irrespective of administration status) or died< 120 days from diagnosis were classified as active WM; while those who were not recommended treatment