PHILADELPHIARemissions induced by gemtuzumab ozogamicin (Mylotarg) monotherapy in patients with first-relapse acute myeloid leukemia (AML) can be prolonged with subsequent therapy. Allogeneic hematopoietic stem cell transplant was particularly effective and even produced some long-term remissions in patients who did not respond to gemtuzumab, Eric Sievers, MD, reported at the 44th Annual Meeting of the American Society of Hematology (ASH abstract 327).
Not a Randomized Trial
The combination of gemtuzumab with allogeneic stem cell transplant appears highly efficacious in patients with first-relapse AML, "with the caveat that this is not a randomized trial, but an observational study of what physicians chose to do with their monotherapy patients in remission," said Dr. Sievers, assistant member, Clinical Research Division, Fred Hutchinson Cancer Research Center.
Allogeneic transplant was relatively safe in patients previously exposed to gemtuzumab, and more than 50% of patients who achieved remission with the combined treatments are alive 2 years post-transplant.
The prognosis for first-relapse AML is historically poor, with response rates to conventional agents of about 30% to 50% and a 6-month median duration of the second remission. Chemotherapy agents are also associated with considerable nonhematologic toxicity.
Dr. Sievers presented long-term follow-up data on patients enrolled in three clinical trials of gemtuzumab, an antibody-targeted chemotherapy consisting of a humanized anti-CD33 antibody linked to calicheamicin, a cytotoxic antibiotic. CD33 is expressed by leukemic blasts in 80% to 90% of patients with AML and is absent from stem cells and nonhematologic tissues, reducing the potential for nonhematologic toxicity.
The aim of the analysis was to determine the best follow-up therapy for patients with relapsed AML treated with gemtuzumab monotherapy. The three multinational trials enrolled a total of 277 patients, all with CD33-positive disease in first untreated relapse.