Tositumomab/iodine-131 tositumomab (Bexxar) is a new radioimmunotherapy active in chemotherapy-relapsed or -refractory indolent (IN) or transformed indolent (TR) non-Hodgkin’s lymphoma. The current study was undertaken to assess overall response rate, duration of response, time to progression, and safety of tositumomab/iodine-131 tositumomab in patients previously treated with the chimeric anti-CD20 antibody rituximab(Drug information on rituximab) (Rituxan).
Eligible patients had a confirmed diagnosis of IN, TR, or de novo follicular large cell (FLC) non-Hodgkin’s lymphoma and progressed after or failed to respond to rituximab. Thirty-eight patients were studied (Stanford , M. D. Anderson , U.S. Oncology ). Histologies included small lymphocytic (1), follicular small cleaved or mixed (25), FLC (3), and transformed (7).
Patient characteristics included a median age of 57 years, four prior chemotherapy regimens (68%), and marrow involvement (32%). Patients received a dosimetric dose (5 mCi iodine-131) and whole-body counts to calculate a therapeutic dose of 75 cGy (platelets > 150,000/µL) or 65 cGy (platelets 100,000 to 149,000/µL). All patients completed the therapeutic dose.
Toxicity was primarily hematologic and transient. Median absolute neutrophil count nadir was 1,200/µL and median platelet nadir was 90,000/µL. The median durations of grade IV neutropenia (6 patients) and thrombocytopenia (4 patients) were 9 and 29 days, respectively. No patients converted 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 were as follows:
Median duration of response was 478 days. Median times to progression for responding and all patients were 566 and 182 days, respectively.
CONCLUSION: In conclusion, tositumomab/iodine-131 tositumomab is a safe and effective treatment strategy for patients who progress after or fail to respond to rituximab.