Long Term Responses to Fludarabine and Rituximab in Waldenstrom’s Macroglobulinemia

Fludarabine and rituximab are commonly used in combination in the treatment of Waldenstrom’s macroglobulinemia (WM), though long term outcome of this regimen remains to be defined. We therefore examined the outcome of 43 WM patients treated on a clinical trial whose eligibility included < 2 prior therapies, and no previous nucleoside analogue or rituximab treatment. Therapy consisted of 6 cycles (25 mg/m²/day for 5 days) of fludarabine and 8 infusions (375 mg/m²/week) of rituximab over 31 weeks. 43 patients were enrolled with a median age of 61, and median prior therapies of 0. Responses were: CR (n=2); VGPR (n=14); PR (n=21); MR (n=4); for an overall and major response rate of 95.3% and 86.0%, respectively. At best response, median bone marrow disease involvement declined from 55% to 5% (p<0.00001), while serum IgM decreased from 3,840 to 443 mg/dL (p<0.00001), and hematocrit rose from 31.2% to 38.0% (p<0.0008). The median time to progression for all patients was 51.2 months, and was longer for untreated versus previously treated patients (77.6 vs. 38.4 months; p=0.017), as well as for those patients who achieved ≥ VGPR versus <VGPR (>88.3 vs. 36.9 months; p=0.049). Grade ≥ 3 toxicities included neutropenia (n=27); thrombocytopenia (n=7); pneumonia (n=6), including two patients who succumbed to non-PCP interstitial pneumonia; peripheral neuropathy (n=2); limbic encephalitis (n=1); hemolytic anemia (n=1). With a median follow-up of 40.3 months, we observed transformation to aggressive lymphoma (n=3); myelodysplasia (n=1); acute myelogenous leukemia (n=2); bladder carcinoma (n=1); and carcinoma of unknown primary (n=1) among 8 patients. The results of this study demonstrate that fludarabine and rituximab is an active regimen in WM, though short and long term toxicities need to be carefully weighed against other available treatment options.