Phase II Trial of CHOP Chemotherapy Followed by Tositumomab/Iodine I-131 Tositumomab for Previously Untreated Follicular Non-Hodgkin's Lymphoma: Five-Year Follow-Up of Southwest Oncology Group Protocol S9911

Abstract

Advanced follicular lymphoma (FL) is incurable with conventional chemotherapy and radiotherapy, and optimal front-line management is controversial. This study was performed to determine the efficacy of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy followed by tositumomab/iodine I-131 tositumomab. From 1999 to 2000, the Southwest Oncology Group (SWOG) conducted a phase II trial (S9911) to test a novel new regimen consisting of six cycles of CHOP chemotherapy followed 4 to 8 weeks later by tositumomab/iodine I-131 tositumomab in 90 eligible patients with previously untreated, advanced-stage FL. The overall response rate was 91%, including a 69% complete remission (CR) rate. After a median follow-up time of 5.1 years, the estimated 5-year overall survival (OS) rate was 87%, and the progression-free survival (PFS) rate was 67%. The 5-year estimates of OS and PFS were each 23% better (absolute difference) than the corresponding figures for patients treated on previous SWOG protocols with CHOP alone. An analysis according to the Follicular Lymphoma International Prognostic Index showed that 21% of patients had high-risk features, 44% had intermediate-risk features, and 34% had low-risk features. High-risk patients had worse OS than lower risk patients (P = .05), but differences in PFS were not statistically significant (P = .21). Serial monitoring of the t(14;18) translocation in bone marrow by polymerase chain reaction demonstrated that 32 of 38 informative patients obtained molecular CRs, including seven patients (18%) after CHOP and 24 additional patients (63%) after tositumomab/iodine I-131 tositumomab. (The timing of conversion of one patient was unclear.) A prospective, phase III, randomized Intergroup Trial is currently underway comparing the efficacy of the promising CHOP + tositumomab/iodine I-131 tositumomab regimen with the efficacy of CHOP + rituximab.