ROCHESTER, MinnesotaIDEC-Y2B8, an anti-CD20 murine monoclonal
antibody (MoAB) conjugated to the radioisotope yttrium-90, appears to
be effective in non-Hodgkins lymphoma (NHL) patients with
splenomegaly, Thomas Witzig, MD, said at an ASH poster session. Some
have considered splenomegaly a contraindication to MoAB therapy
because of theoretical concerns about the spleen acting as an
antibody sink, limiting efficacy.
Dr. Witzig, of the Mayo Clinic, and his colleagues looked at a subset
of eight patients with spleno-megaly treated with IDEC-Y2B8 in phase
I/II trials of the agent in patients with relapsed or refractory low-
or intermediate-grade NHL.
They found that 88% of splenomegaly patients (7/8) had a response in
the spleen, including a complete response (CR) in six patients (75%).
The overall response rate in these patients was 50% (4/8), including
two CRs. This was not significantly different from the 70% overall
response (30/43), seen in patients without splenomegaly
Overall, among the 58 study patients, the response rate to IDEC-Y2B8
at all doses was 67% (25% CR); in patients with low-grade disease, it
was 82% (27% CR), and in those with intermdiate-grade disease, 43%
Gregory Wiseman, MD, of the Mayo Clinic, reported safety findings
from the study. Weve seen no major organ toxicity, and at
all doses, the dose to the normal organs has been quite low in terms
of what would be considered toxic with external beam radiation,
he said. In general, IDEC-Y2B8 is probably less toxic than
external beam even at the same dose.
Dr. Wiseman said that hematologic toxicity has been reversible.
We have not had anyone who developed any prolonged
cytopenia. Although some patients have required platelet
transfusions, there have been no bleeding problems, and only three
patients (6%) have been hospitalized for infection. They all
recovered with appropriate treatment, he said.
He pointed out that infection rates and blood count drops are
similar to what would occur with chemotherapy-based regimens, but the
response rate with IDEC-Y2B8 in this group of heavily pretreated
patients is better than we would see with chemotherapy.
An ongoing randomized phase III trial is comparing IDEC-Y2B8 with the
unlabeled anti-CD20 chimeric MoAB rituximab (Rituxan). Another
ongoing trial is looking at the radiolabeled agent in patients who
have not responded to or are refractory to rituximab.