SAN FRANCISCOIodine 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 chemotherapy42% 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.