A New Prognostic Index for Waldenström Macroglobulinemia Based on a Multicenter Retrospective Study of the Japanese Society of Myeloma

Background: We recently reported that the International Prognostic Scoring System for Waldenström macroglobulinemia (ISSWM), which is widely used to predict the prognosis of WM patients, might not be applicable to Japanese patients, and evidence of pleural effusion might be a novel adverse prognostic factor for symptomatic WM in the rituximab era. Further studies with a large number of patients are deemed to be conducted.

Methods: We retrospectively analyzed the clinical data of 498 patients with WM diagnosed between January 2001 and December 2015 from 44 institutes involved with the Japanese Society of Myeloma. The overall survival (OS) was analyzed using Kaplan-Meier methods and compared using log-rank test. Several clinical characteristics at the diagnosis were assessed by Cox regression for univariate and multivariate analyses of the OS.

Results: We included 420 cases diagnosed with symptomatic (n=314) and asymptomatic WM (n=106) in accordance with the classification of the Second International Workshop on WM. The median age at the diagnosis was 69 (range, 32-91) years, with 75.5% male, and 16.0% had an Eastern Cooperative Oncology Group performance status (ECOG PS) of 2-4. Oral alkylating agents, purine analogs, cyclophosphamide, doxorubicin, vincristine and prednisolone (CHOP) or CHOP-like regimens ± rituximab, rituximab monotherapy, or dexamethasone, rituximab and cyclophosphamide (DRC) were mainly administered as initial treatment. Rituximab-containing therapy was administered in 76.8% of all patients. The median follow-up was 45 months. The 5-year OS rate for all patients was 77.9%, while the rates for those with symptomatic and asymptomatic WM were 72.9% and 92.2%, respectively. Significant differences in the survival were seen between risk groups of ISSWM in symptomatic WM patients (5-year OS: high, 55.4%; intermediate, 81.2%; low, 90.2%; p<0.0001) (Figure 1). A univariate analysis showed that age >65 years, platelet count ≤10×10⁴/µL, serum β2-microglobulin (β2-MG) >3 mg/L, ECOG PS 2-4, abnormal karyotype, pleural involvement, WBC <4000/µL, amyloidosis, fluid retention, pleural effusion, ascites, serum albumin ≤3.5 g/dL, serum creatinine >1.5 mg/dL, CRP >2.0 mg/dL and sIL-2R >4000 U/mL were significant adverse prognostic factors for the OS. A multivariate analysis revealed that a platelet count ≤10×10⁴/µL (hazard ratio [HR] 5.942; 95% confidence interval [CI] 2.265-14.761), serum β2-MG >3 mg/L (HR 2.748; 95% CI 1.091-7.655), ECOG PS 2-4 (HR 2.899; 95% CI 1.219-6.290), and pleural involvement (HR 11.066; 95% CI 3.672-29.829) were adverse independent risk factors for symptomatic WM. We constructed a prognostic model by combining these prognostic variables as follows: patients with good risk (n=219), no adverse factors or only serum β2-MG >3 mg/L or ECOG PS 2-4; patients with poor risk (n=81), ≥1 adverse factors with a platelet count ≤10×10⁴/µL, pleural involvement, or both serum β2-MG >3 mg/L and ECOG PS 2-4. The 5-year OS rates were 82.3% for good risk and 44.4% for poor risk, and this prognostic model significantly stratified symptomatic WM patients separately by the survival (p<0.0001) (Figure 2). The survival of patients with both poor risk in our model and high risk in ISSWM were extremely poor (5-year OS: poor and high [n=57], 24.7%; poor and intermediate [n=14], 80.0%; poor and low [n=2], not available; p=0.0031). In contrast, no significant differences were observed for the survival for the ISSWM risk groups in patients with good risk in our model (5-year OS: good and high [n=69], 76.0%; good and intermediate [n=83], 81.6%; good and low [n=42], 89.5%; p=0.2045).

Conclusion: Although ISSWM may be useful for survival risk stratification in Japanese patients, we found that intermediate- and high-risk patients seemed to have a better prognosis than those in Western studies in the rituximab era (Dimopoulos MA, et al. Haematologica. 2008; 93: 1420-22). Thrombocytopenia and pleural involvement were found to be strong adverse prognostic factors in symptomatic WM, and our new prognostic index including them was easy to use in daily clinical practice and superior to ISSWM for detecting high-risk patients. Further studies are warranted to validate our prognostic index, especially in the era of novel agents.

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