An experimental cancer vaccine from GlaxoSmithKline failed to meet the first of two joint targets in a closely watched late-stage clinical trial, dealing a blow to the high-risk, high-reward project.

Britain’s biggest drugmaker said it would continue with the Phase III trial of its MAGE-A3 therapeutic vaccine until the second of the targets, known as co-primary endpoints, is assessed.

The vaccine is one of two particularly high-risk developmental GSK products believed by analysts to have the potential to become multibillion-dollar sellers. The other is a heart drug called darapladib, designed to fight clogged arteries in a different way to statins.

Unlike traditional preventative vaccines, MAGE-A3 is meant to treat people with established disease, where it is supposed to help their immune systems to fight back. It is also being tested in lung cancer.

Other companies have had some recent notable success in clinical trials with innovative drugs to boost the immune system, but GSK is still pushing the scientific boundaries with MAGE-A3.

GSK’s vaccine was developed for use in patients with tumours that express the cancer-related MAGE-A3 gene, which occurs in about 65 per cent of Stage III melanomas.

It failed to significantly extend disease-free survival when compared with placebo in this population in the Phase III study.

The second endpoint of the trial is to see whether disease-free survival is improved in a subset of MAGE-A3-positive patients. Results from this analysis are expected in 2015.

GSK added that no safety issues had emerged in the trial.

“We remain committed to identifying a patient sub-population who may benefit from this investigational treatment,” said Vincent Brichard, head of immunotherapeutics at GSK Vaccines.

GSK is also continuing to study MAGE-A3 in another Phase III study against non-small cell lung cancer. The first data from this trial are expected in the first half of 2014. (Reuters)