Tositumomab/Iodine-131 Tositumomab for Non-Hodgkin’s Lymphoma Patients Who Progressed After Treatment With Rituximab: Results of a Multicenter Phase II Study

Tositumomab/iodine-131 tositumomab (Bexxar) is a newradioimmunotherapy active in chemotherapy-relapsed or -refractory indolent (IN)or transformed indolent (TR) non-Hodgkin’s lymphoma. The current study wasundertaken to assess overall response rate, duration of response, time toprogression, and safety of tositumomab/iodine-131 tositumomab in patientspreviously treated with the chimeric anti-CD20 antibody rituximab (Rituxan).

Eligible patients had a confirmed diagnosis of IN, TR, or denovo follicular large cell (FLC) non-Hodgkin’s lymphoma and progressed afteror failed to respond to rituximab. Thirty-eight patients were studied (Stanford[15], M. D. Anderson [13], U.S. Oncology [10]). Histologies included smalllymphocytic (1), follicular small cleaved or mixed (25), FLC (3), andtransformed (7).

Patient characteristics included a median age of 57 years, fourprior chemotherapy regimens (68%), and marrow involvement (32%). Patientsreceived a dosimetric dose (5 mCi iodine-131) and whole-body counts to calculatea therapeutic dose of 75 cGy (platelets > 150,000/µL) or 65 cGy (platelets100,000 to 149,000/µL). All patients completed the therapeutic dose.

Toxicity was primarily hematologic and transient. Medianabsolute neutrophil count nadir was 1,200/µL and median platelet nadir was90,000/µL. The median durations of grade IV neutropenia (6 patients) andthrombocytopenia (4 patients) were 9 and 29 days, respectively. No patientsconverted to human antimouse antibody-positivity after the therapeutic dose.Investigator-assessed confirmed responses to tositumomab/iodine-131 tositumomab(at least two assessments 4 weeks apart) by prior treatment with rituximab wereas follows:

Median duration of response was 478 days. Median times toprogression for responding and all patients were 566 and 182 days, respectively.

CONCLUSION: In conclusion, tositumomab/iodine-131 tositumomab isa safe and effective treatment strategy for patients who progress after or failto respond to rituximab.

Click here to read Dr. Bruce Cheson's commentary on this abstract.