Pfizer withdraws cancer drug

Pfizer has withdrawn from the US market its acute myeloid leukaemia (AML) drug Mylotarg (gemtuzumab ozogamicin) after post-marketing data failed to demonstrate efficacy and showed that the drug's risks were higher than they appeared in earlier studies.

Mylotarg has been sold in the US for a decade, following clearance in May 2000 under the US Food and Drug Administration's (FDA) accelerated approval program, which allows the marketing of certain medications based on surrogate endpoints, or laboratory measurements used in place of actual clinical outcomes.

The drug was submitted to the FDA by Wyeth, which has since merged with Pfizer, and was cleared for marketing based on data from just 142 AML patients. The subjects were tested in studies that used the surrogate endpoint of response rate (the percentage of patients whose leukaemia decreased or disappeared in laboratory tests) rather than clinical survival data.

Companies must conduct post-marketing studies for drugs that receive accelerated approval, with the understanding that if the studies are not carried out or are not successful, the drug will be pulled from the market.

Wyeth began a trial in 2004 to determine whether adding Mylotarg to standard chemotherapy demonstrated an improvement in survival time, and halted the study early when no improvement in clinical benefit was observed and more deaths occurred in the Mylotarg group than in the group receiving chemotherapy alone.

Post-marketing data also has shown that the rate of veno-occulusive disease, a serious liver condition that was linked to the drug in the premarket trials, is higher than was thought.

The withdrawal was conducted voluntarily by Pfizer following a request from the FDA. Pfizer said it is also in discussions about the drug with regulatory bodies outside the US.