Gemtuzumab ozogamicin, which was discontinued in the United States in 2010, reduced relapse risk and improved survival with little increase in toxicity when added to induction chemotherapy in older Welsh patients with acute myeloid leukemia (AML).

OG is an antibody conjugate. The action of this class of drugs involves attaching chemotherapy molecules to antibodies specifically designed to recognize proteins on the surface of cancer cells and target those cells, leaving healthy cells unharmed, as explained in a statement from Cardiff University in Cardiff, Wales. The study’s chief investigator, Professor Alan Burnett, is based at the university’s School of Medicine.

The FDA granted accelerated approval to OG under the brand name Mylotarg in 2000, for persons aged 60 years and older with AML who were experiencing their first leukemia relapse and who were not considered candidates for other cytotoxic therapy. Ten years later, Pfizer Inc. voluntarily withdrew Mylotarg from the market after an interim analysis revealed a lack of evidence of efficacy, a significantly higher rate of fatal induction-phase toxicity than seen in patients not receiving the drug, and serious hepatotoxicity.

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In Burnett’s study, 1,115 persons aged 51 to 84 years (median age 67 years) with untreated AML or high-risk myelodysplastic syndrome were randomized to receive standard induction chemotherapy administered with (559 patients) or without (556 patients) GO 3 mg/m2 on day 1 of the first course of therapy. Induction chemotherapy consisted of either daunorubicin/ara-C or daunorubicin/clofarabine.

The overall response rate was 69%, with no difference between the GO and no-GO arms. There was also no difference in 30- or 60-day mortality between the two groups, and no major increase in toxicity with GO.

However, with median follow-up of 30 months (range 5.5 to 54.6 months), 3-year cumulative incidence of relapse was significantly lower with GO (68% vs 76%), and 3-year survival was significantly better (25% vs. 20%), the researchers reported in Journal of Clinical Oncology (2012;30[32]:3924-3931).

“Although there has been some controversy around the use of GO following its withdrawal in the United States two years ago, these results appear extremely promising and suggest no such cause for concern if the appropriate dose is given,” commented Burnett in the Cardiff University statement. “Crucially, this represents some of the first progress in treating AML patients of this age group for at least 20 years.”