Iodine I 131 Tositumomab Achieves Remissions in One Third of NHL Patients

SAN FRANCISCO—Iodine I 131 tositumomab (Bexxar) attains complete remission in more than one third of non-Hodgkin’s lymphoma (NHL) patients, and these responses can last several years, according to a 10-year study.

"After a 1-week course of treatment with Bexxar, patients can have years of remission," reported lead researcher John P. Leonard, MD, clinical director of the Center for Lymphoma and Myeloma at Weill Medical College at Columbia University in New York, New York.

Iodine I 131 tositumomab is a radiolabeled monoclonal antibody that attaches to a target marker on NHL cells. As a result, an immune response occurs and the antibody delivers a lethal dose of iodine 131 radiation to the tumor cells.

Before embarking on the study, Dr. Leonard and other researchers knew that iodine I 131 tositumomab was able to produce a complete response in some patients. But it was unclear how long remissions were lasting. That was the rationale behind the study, which reviewed data on 251 patients with low-grade or transformed low-grade NHL who had received iodine I 131 tositumomab over the last 10 years.

Participants included previously untreated, refractory, and heavily pretreated patients. Seventy percent were less than 60 years old and 56% were male. Stage III or IV disease was present in 89% at protocol entry; 46% had positive bone marrow involvement; and 32% bulky disease.

35% Complete Response Rate

In this diverse patient population, iodine I 131 tositumomab produced an overall 35% complete response rate. Previously untreated patients experienced an even higher complete response rate of 58%. Most patients in the study, however, had relapsed after chemotherapy—42% had received one to three prior regimens of chemotherapy and 33% had received four or more prior regimens.

But even these patients achieved significant numbers of complete remissions on iodine I 131 tositumomab. Thirty-two percent of patients who had undergone one to three previous chemotherapy regimens achieved a complete response for a median duration of 20 months and 24% of those heavily pretreated with more than four regimens had a response rate of 24% with a median duration of 19 months.

Iodine I 131 tositumomab also worked well in patients with poor prognoses, including elevated lactate dehydrogenase (LDH), bone marrow involvement, and bulky disease. Those with bulky disease, for instance, had a complete response rate of 21% for a median duration of 22 months.

Good Perspective

"Our research revealed that Bexxar can be effective in all situations," Dr. Leonard said. "The study thus gave us a good perspective on the potential versitality of the drug."

The complete response was higher and the duration of complete response was longer when used earlier in therapy. The median duration of complete response had not been reached at the time the study was reported, indicating that the majority of patients are continuing to respond.

In another study, iodine I 131 tositumomab was shown to be effective in patients with low-grade, transformed low-grade, or follicular large-cell NHL who failed to respond to or had progressed following rituximab treatment. 

"Our 10-year analysis, along with the data from patients who have been refractory to or relapsed from rituximab, emphasize the potential role of Bexxar for patients with NHL at various points in their disease course," Dr. Leonard said. He hopes to further evaluate the drug’s effectiveness in follow-up studies, he added.