Approximately one-third of patients with Waldenström macroglobulinemia (WM) experience a deepening of response after completing a rituximab-containing treatment regimen, according to research published in the American Journal of Hematology. This deepening of response may be linked to improved progression-free survival (PFS) and survival after frontline treatment initiation (SAFTI).

WM response is determined by whether a therapy induces a decrease in serum immunoglobulin (Ig) M levels. There is some evidence that rituximab-containing regimens are linked to continual decreases in IgM months, or even years, after treatment completion.

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For this retrospective cohort study, researchers attempted to determine the rate of response after rituximab treatment, as well as factors that might predict this, among patients with WM. PFS and SAFTI rates among those with a deepened post-treatment response were also evaluated, defined as at least a 25% decrease in serum IgM levels.

Of 178 included patients, 116 (65%) received maintenance therapy and 62 (35%) underwent observation after induction with a rituximab-containing regimen. Characteristics were balanced between those who underwent maintenance therapy and those under observation.

In the maintenance group, 44 (38%) patients had a deepened response after therapy; median time from completion of therapy to lowest serum IgM level was 1.6 years (range, 0.1-7.9). In the observation group, 19 (31%) patients had a post-therapy deepened response, with a median time to lowest IgM level of 1.6 years (range, 0.2-5.1 years).

Patients with a baseline hemoglobin level of less than 11.5 g/dL (odds ratio [OR], 0.44; P =.02), bone marrow involvement of at least 50% (OR, 0.49; P =.03), CXCR4 mutations (OR, 0.33; P =.03), or IgM levels of at least 4000 mg/dL (OR, 0.53; P =.045) were less likely to have a deepened response after therapy.

A post-therapy deepened response was associated with both improved PFS (hazard ratio, 0.46; P =.006) and improved SAFTI (hazard ratio, 0.21; P =.01).

“We present a novel phenomenon of deepening of response after completion of therapy that can be associated with better PFS and SAFTI in WM patients,” the researchers wrote.

Disclosures: Some authors have declared affiliations with the pharmaceutical industry. Please refer to the original study for a full list of disclosures.

Reference

1.     Castillo JJ, Gustine JN, Keezer A, et al. Deepening of response after completing rituximab-containing therapy in patients with Waldenstrom macroglobulinemia [published online December 23, 2019]. Am J Hematol. doi:10.1002/ajh.25712