US regulators have issued a green light for Pfizer’s Mylotarg as a treatment for acute myeloid leukaemia (AML), seven years after the drug was with voluntarily withdrawn from the market.

The US Food and Drug Administration has cleared use of Mylotarg (gemtuzumab ozogamicin) to treat adults with newly diagnosed AML whose tumours express the CD33 antigen, as well as for those aged two years and older who have experienced a relapse or who have not responded to initial treatment (refractory).

The drug originally received accelerated approval in May 2000 as a stand-alone treatment for older patients with CD33-positive AML who had experienced a relapse, but was taken off the market in 2010 after subsequent confirmatory trials failed to verify clinical benefit and demonstrated safety concerns, including a high number of early deaths.

On the back of new data, the new approval includes a lower recommended dose, a different schedule in combination with chemotherapy or on its own, and a new patient population.

In one trial, patients who received Mylotarg survived longer than those who received only best supportive care, with median overall survival 4.9 months versus 3.6 months. Data from another showed that following treatment with the drug, 26 percent of patients achieved a complete remission that lasted a median 11.6 months.

“We are approving Mylotarg after a careful review of the new dosing regimen, which has shown that the benefits of this treatment outweigh the risk,” said Richard Pazdur, director of the FDA’s Oncology Center of Excellence and acting director of the Office of Hematology and Oncology Products in the FDA’s Center for Drug Evaluation and Research.

“Mylotarg’s history underscores the importance of examining alternative dosing, scheduling, and administration of therapies for patients with cancer, especially in those who may be most vulnerable to the side effects of treatment.”

The drug is a targeted therapy that consists of an antibody connected to an anti-tumor agent that is toxic to cells, thought to work by taking the anti-tumour agent to the AML cells that express the CD33 antigen, blocking the growth of cancerous cells and causing cell death.

“The FDA approval of Mylotarg fills a critical unmet need for many adults and children with AML, which can be fatal in a matter of months or even weeks if not treated and has a high relapse rate,” said Liz Barrett, global president, Pfizer Oncology. “Based on clinical data, real-world experience and support from the AML community, we are grateful Mylotarg now has the potential to help a broad range of AML patients.”