IgM-Gammopathies Transformed into Aggressive Lymphoma: Incidence, Basal Clinical Features and Outcome of a Registry Based, Spanish Retrospective Series

Background

Transformation into aggressive lymphoma (AL) is a rare complication of indolent lymphoproliferative disorders (LPDs) and is characterized by poor outcome. Immunoglobulin M (IgM) gammopathies are a spectrum of conditions, from monoclonal gammopathy of undetermined significance (MGUS) to Asymptomatic Waldenstroem Macroglobulinemia (AWM) and Symptomatic WM (SWM) that can eventually evolve to transformed WM (tWM). Actually, tWM represents a clinical challenge, mainly because of its poor characterization.

Aims

This registry study aims to better characterize tWM, focusing on prognostic factors heralding transformation to AL.

Methods

Two registries of IgM-MGUS, AWM and SWM [Owen, Semin Oncol 2003] based in Salamanca and in the region of Castilla and Leon (Spain) were investigated to identify cases with histological transformation. IgM-secreting patients with other LPDs (e.g. chronic lymphocytic leukemia, marginal zone lymphoma, IgM-multiple myeloma) were excluded from the analysis. All patients provided written informed consent in accordance to Helsinki's declaration. Statistical analysis was carried out using R v 3.3.3. tool; survival analyses were performed with Log-Rank method, while group comparison was performed with t-student for continuous variables and Chi-square tests for categorical variables.

Results

Data from 903 patients with IgM-secreting disorders diagnosed between 1976 and 2019 were analyzed; 587 cases with confirmed diagnosis of IgM-MGUS, AWM or SWM were selected. Out of 587 IgM-gammopathies, 22 cases with histological transformation to AL were identified. Cumulative incidence of tWM was: 1.4% at 5, 3.4% at 10 and 5.3% at 12 years, respectively (figure 1). Clinical features at first diagnosis of patients subsequently developing tWM where then analyzed: 3/22 tWM evolved from previous IgM-MGUS, while the remaining patients originally presented with AWM (6/22) or SWM (13/22). IPSS-WM prognostic score was LR for 5, IR for 12 and HR for 3/20 patients, respectively [Morel, Blood 2009]. Glancing on distributions between groups according to the outcome, tWM differed from not transformed (NT) cases for: lower median age at diagnosis (66 vs 72 years, p=0.018), lower platelets levels (median 188 vs 235 x 10^9/mmc, p=0.017), higher LDH ratio (0.8 vs 0.67, p=0.015), higher incidence of chromosome 6q deletion by FISH (40 vs 14%, p=0.021) and higher clonal B lymphocytes infiltration on marrow aspirate by flow cytometry (15 vs 4.5%, p= 0.022). Moreover, 13/22 patients received anti-WM treatment within 3 months from initial diagnosis, mainly chlorambucil-based; 5/22 patients received rituximab in first line and 13 in second line. From the whole series, after a median follow-up of 80 months, median transformation-free survival was 61 months from initial diagnosis (range: 0-228). Among these, Only 1/22 of tWM patient is still alive; 19/21 deaths were thus related to AL/WM, with a median survival after transformation of 12 months (0-53). In the whole series (n=587), median OS from initial diagnosis of IgM gammopathy was 76 months for the tWM group (6-225), that is shorter than the NT group (128 months, p=0.012, figure 2). Focusing only on patients treated at initial diagnosis, median survival after first treatment (SAFTI) was 62 vs 90 months for tWM vs NT (p=0.011, figure 3), and median time to next treatment was 28 vs 46 months, respectively (p=0.13). Overall, 10/22 tWM patients received ≥3 treatment lines, and median number of lines prior to transformation was 2 (0-3). Finally, in the whole series IPSS-WM score at diagnosis confirmed to impact on survival (median OS=151, 119 and 56 months for LR, IR and HR groups, respectively, p <0.001). However, this was not the case for tWM cases only, where OS was no longer different between groups.

Conclusions

In this retrospective study, we confirmed dismal outcome for tWM patients; incidence of transformation was comparable to expectations at 5 years, but higher at subsequent follow-up. At initial diagnosis of IgM gammopathy, younger age, low platelets level, high LDH ratio, high B lymphocytes infiltration by flow cytometry and presence of 6q deletion were significantly enriched among patients subsequently developing tWM. IPSS-WM score looked less predictive among tWM patients probably given to the limited numbers of tWM series. Novel prognostic tools are eagerly awaited for tWM patients.

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