RIT Safe, Effective in Elderly and Poor-Prognosis Patients

SAN FRANCISCO—Radioimmunotherapy (RIT) with the investigational radiolabeled monoclonal antibody known as Bexxar (tositumomab and iodine I-131 tositumomab) is effective and well tolerated in non-Hodgkin’s lymphoma (NHL) patients with poor prognostic features, according to retrospective analyses presented at the 37th Annual Meeting of the American Society of Clinical Oncology (ASCO).

In one analysis (abstract 1140), investigators looked at a cohort of 251 patients enrolled in phase I-III trials between 1990 and 1999. Overall response rate was 74%, with a 35% complete response rate. For the subset of poor-prognosis patients in that group (ie, those with transformed low-grade NHL, bulky disease, no response to previous chemotherapy, four or more prior chemotherapies, or prior radiation treatment), overall response rates were approximately 60%, with complete response rates of 20% to 25% and median duration of response up to 9 months.

A separate study (abstract 1136) showed that elderly NHL patients tolerated tositumomab treatment. In the retrospective analysis, which included 70 patients more than 60 years of age, adverse events and other safety outcomes were not much different than what might be expected in younger patients.

"This study showed that elderly patients tolerate the drug very well," said Stephanie A. Gregory, MD, director of hematology, Rush-Presbyterian-St. Luke’s Medical Center, Chicago. "The response rates are slightly less than those seen with younger patients, but you might expect that because of age and co-morbid conditions."

Overall response among these elderly patients was 60% vs 76% for a cohort of 216 patients younger than 60 who had also participated in prior Bexxar trials. The median duration of response was 9 months for the elderly patients vs 13 months for the younger patients. Complete response was seen in 20% and 37% of old and young patients, respectively.

Twenty-one patients were older than 70 years. For that subset, overall response was 48% (14% complete response rate), with a median duration of response of 11 months.

Bexxar is given as a single therapeutic dose specific to each patient’s clearance of the antibody, as determined by a prior dosimetric dose. The treatment combines the antitumor mechanisms of unlabeled tositumomab antibody with targeted radiotherapy provided by iodine I-131 tositumomab.

Re-treatment Protocol

Dr. Gregory noted that a Bexxar re-treatment protocol has been developed. for NHL patients who did not have a positive human antimouse antibody (HAMA) reaction following the first treatment. Reported at ASCO (abstract 1139) were 18 patients who progressed after responding to Bexxar and were given a second treatment.

Twelve patients responded to re-treatment with Bexxar (median duration, 11 months). Half of the responders had a complete response (median duration, not reached). As of the ASCO meeting, three of these patients had ongoing responses 20 to 56 months in duration. One patient developed a HAMA reaction.

"We’re finding the efficacy is very similar with re-treatment," Dr. Gregory said. "If patients respond the first time, they often respond the second time."