Progression Risk-Based Classification of Asymptomatic Waldenström Macroglobulinemia

Background. Waldenström macroglobulinemia (WM) is a low-grade non-Hodgkin's lymphoplasmacytic lymphoma associated with overproduction of monoclonal IgM protein. It is preceded by an asymptomatic stage, called Smoldering Waldenström Macroglobulinemia (SWM), associated with a high risk of progression to overt disease. Current understanding of progression risk in SWM is based on a few small studies, and it is still unclear how to distinguish the asymptomatic patients who will progress from those who will not.

Patients and Methods. We obtained clinical data of all WM patients who had been diagnosed and followed up at Dana-Farber Cancer Institute from 1982 to the end of 2014. Only patients with asymptomatic disease at the time of diagnosis were included in this study to identify risk factors for disease progression. Patients who received chemotherapy for a second cancer, before or after asymptomatic WM diagnosis (n =24), were excluded as chemotherapy might have affected the natural course of disease. Patients who progressed to or were diagnosed later with other types of B-cell lymphoproliferative disorders or Amyloidosis (n =71) and patients with myeloproliferative disorders or thalassemia (n = 4) were all excluded from our cohort. Furthermore, we excluded patients with no morphologic evidence of lymphoplasmacytic infiltration in the bone marrow biopsy (n =37), those without a bone marrow biopsy done at time of diagnosis (n =21), and those who were treated for peripheral neuropathy alone (n =13). Progression was defined based on the Consensus Panel recommendations of the Second International Workshop on WM. Survival analysis was performed using the Kaplan-Meier method and differences between the curves were tested by log-rank test. Effects of potential risk factors on progression rates was examined using Cox proportional-hazards models, with hazard ratios (HRs) and associated 95% confidence intervals (CIs).

Results. A total of 439 patients were included in the study. During the 35-year study period and a median follow up of 7.8 years, 317 patients (72.2%) progressed to symptomatic WM. The median time to progression was 3.9 (95% CI 3.2-4.6) years. In the multivariate analysis, IgM ≥ 4,500 mg/dL (adjusted HR 4.65; 95% CI 2.52-8.58; p < 0.001), BM lymphoplasmacytic infiltration ≥ 70% (adjusted HR 2.56; 95% CI 1.69-3.87; p < 0.001), β2-microglobulin ≥ 4.0 mg/dL (adjusted HR 2.31; 95% CI 1.19-4.49; p = 0.014), and albumin < 3.5 g/dL (adjusted HR 2.78; 95% CI 1.52-5.09; p = 0.001) were all identified as independent predictors of disease progression, suggesting those thresholds could be clinically useful for determining high-risk patients. On the other hand, given the continuous nature of these variables, we built a proportional hazards model based on four variables (Bone marrow infiltration percentage, serum IgM, albumin, β2-microglobulin). The model divided the cohort into 3 distinct risk groups: a high-risk group with a median time to progression (TTP) of 1.9 years (95% CI 1.64-2.13), an intermediate-risk group with median TTP of 4.6 years (95% CI 4.31-5.15), and a low-risk group with a median TTP of 8.1 years (95% CI 7.33-8.13)(See Figure). To enhance its clinical applicability, we made the model available as user interface through a webpage and mobile application, where clinicians can enter an individual SWM patient's lab values and get information regarding their risk group and estimated individual risk of progression to symptomatic WM.

Conclusion. We have assembled the largest cohort of SWM patients to date, which allowed us to identify four independent predictors of progression to overt disease: BM infiltration ≥ 70%, IgM ≥ 4,500 mg/dL, b2m ≥ 4.0 mg/dL and albumin < 3.5 g/dL. Using those variables in a proportional hazards model, we developed a robust, flexible classification system based on risk of progression to symptomatic WM. This system stratifies SWM patients into low-, intermediate- and high-risk groups and thus has the potential to inform patient monitoring and care. Most importantly, it can help identify high-risk patients who might benefit from early intervention in this rare malignancy.

Figure 1.

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Figure 1.

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