Results from a phase 3 trial showed that first-line monotherapy with low-dose gemtuzumab ozogamicin appeared to be superior to best supportive care in older patients with acute myeloid leukemia (AML) who were ineligible for intensive chemotherapy.1

Gemtuzumab ozogamicin targets myeloid cells via the CD33 epitope and combines a humanized anti-CD33 monoclonal antibody with the DNA intercalator calicheamicin. An Italian study that included 237 patients found that gemtuzumab ozogamicin may significantly improve overall survival compared to best supportive care. In addition, the study found that it produced no unexpected adverse events and toxicity was manageable.

Eunice Wang, MD, who is chief of leukemia service and a professor of oncology in the Department of Medicine at Roswell Park Cancer Institute in Buffalo, NY, said these findings are encouraging but she cautioned that this is only one study and in some respects the results are a bit unexpected.

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“This study highlights the potential therapeutic benefit of antibody-drug conjugates (ADCs) similar to gemtuzumab ozogamicin for AML therapy. Although gemtuzumab ozogamicin was previously FDA-approved for relapsed AML, this agent was subsequently withdrawn from the market due to questions of toxicity when combined with chemotherapy in younger AML patients. It is therefore somewhat surprising to learn that low doses of this same ADC as monotherapy in older individuals with AML would be so beneficial and well tolerated,” she told Cancer Therapy Advisor.

Sergio Amadori, MD, Tor Vergata University Hospital in Rome, Italy, and colleagues compared single-agent gemtuzumab ozogamicin  with best supportive care, including hydroxyurea as first-line therapy in older patients with AML unsuitable for intensive chemotherapy.

All patients were at least 61 years old and 118 were randomized to receive a single induction course of gemtuzumab ozogamicin  (6 mg/m2 on day 1 and 3 mg/m2 on day 8); 119 were randomized to best supportive care.

Median age was 77 years (range: 62 to 88 years) and approximately two-thirds of patients were 76 or older. Patients who did not progress after gemtuzumab ozogamicin  induction were allowed to receive up to 8 monthly infusions of gemtuzumab ozogamicin  at 2 mg/m2.

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The study’s primary endpoint was overall survival by intention-to-treat analysis and the researchers found that the median overall survival was 4.9 months (range: 4.2 to 6.8 months) in the gemtuzumab ozogamicin treatment arm compared to 3.6 months (range: 2.6 to 4.2 months) in the best supportive care group (HR, 0.69). One-year overall survival rate was 24.3% for patients in the gemtuzumab ozogamicin  treatment arm compared to only 9.7% in the best supportive care treatment arm.