Tositumomab and Iodine I-131 Tositumomab for Previously Untreated, Advanced-Stage, Follicular Lymphoma: Median 10 Year Follow-up Results.

Tositumomab and iodine I 131 tositumomab (Bexxar® Therapeutic Regimen) has been found effective in relapsed/refractory follicular lymphoma. We now report updated results of a single center, single-arm, Phase II trial of a single one-week course of this treatment for 76 previously untreated, stage III and IV, follicular lymphoma patients (reporting period June 1996 to May 2009).

Patients had a median age of 49 years (range 23 to 69) and received a dosimetric dose followed by a single total body dose of 75 cGy iodine I-131 tositumomab one week later. Seventy percent had stage IV disease and 70% of patients had histological grade 1 follicular lymphoma, 29% had grade 2, and 1 patient had mantle-cell lymphoma. Bone marrow involvement was present in 64% of patients; 43% of patients had at least one tumor ³ 5 cm in diameter; LDH was elevated in 30%. Overall, 35% of patients had high risk Follicular Lymphoma International Prognostic Index (FLIPI) scores and 50% had intermediate risk scores. Patients entered long-term follow-up after disease progression or after 2 years on study. Response, second malignancy occurrence and thyroid medication use were assessed every 6 months for 5 years and yearly thereafter up to 12 years post treatment.

As previously reported (NEJM 352:441, 2005), the overall response rate was 97% with 57 patients (75%) achieving a complete remission. Hematologic toxicity, although common, was modest to moderate (grade 4 neutropenia in 5% of patients and no grade 4 thrombocytopenia). After a median of 10 years follow-up (range 0.7 to 12.3 years), the median duration of response was 6 years (95% CI: 2.5, 10.8), with approximately 40% remaining progression-free at 10 years. For the 57 complete responders, median progression-free survival was 10.9 years (95% CI: 8.3, NR). Ten-year overall survival was approximately 82%. Five cases (7%) of hypothyroidism occurred 0.5 to 2.9 years after treatment and were managed with thyroid hormone replacement. Eleven patients (14%) were diagnosed with second malignancies including 4 skin neoplasms (2 basal cell and 2 squamous cell) and 7 visceral neoplasms (3 breast, 2 prostate, 1 endometrial cancer, 1 glioblastoma). One case of myelodsyplastic syndrome was diagnosed about 8 years after treatment.

A single course of treatment with Bexxar therapeutic regimen can commonly produce durable responses, especially durable complete responses lasting over a decade in patients with untreated follicular lymphoma. Further studies comparing this monotherapy to other regimens, including combination therapies, are warranted.

Kaminski:GlaxoSmithKline: Honoraria, Patents & Royalties, Research Funding, Speakers Bureau. Off Label Use: Radioimmunotherapeutic for treatment of frontline treatment of follicular lymphoma. On-label use is for relapsed/refractory patients. Horner:GlaxoSmithKline: Employment. Williams:GlaxoSmithKline: Employment. Vleisides:GlaxoSmithKline: Employment. Wahl:Nordion: Honoraria; GlaxoSmithKline: Patents & Royalties.