AstraZeneca (NYSE: AZN) has gained support for its cancer drug vandetanib from European regulators, paving the way for a potential approval of the drug in the EU for advanced forms medullary thyroid cancer. However, the drug -- once a blockbuster hopeful that garnered U.S. approval for MTC in April -- has been knocked down a few notches.

The European Medicines Agency backed AZ's application for approval of the drug, a kinase inhibitor, for treating patients with aggressive and inoperable cases of MTC, the least common of the four types of thyroid cancer. They threw their support behind vandetanib after reviewing data from a late-stage study of 331 patients with aggressive MTC that had spread to other organs. Patients on the drug had a 54% reduction in risk of the disease getting worse than those in the placebo camp.

However, European regulators recommended the approval come with a caveat that MTC patients whose RET mutation status is negative or unknown might not benefit from the drug as much as those with the mutation. AstraZeneca said clinical trials show the drug benefits the non-RET set of patients, but it's planning another study to provide more evidence of that.

With a U.S. approval already in place, analysts expect annual sales of the drug, marketed as Caprelsa, to hit $112 million in five years, Reuters reported. That's a far fall from the earlier blockbuster figures industry watchers were predicting when the drug was still in the running to treat the big non-small cell lung cancer population. The drug failed to succeed in clinical trials involving patients with lung cancer.

The European Commission now gets the final say on whether the drug gains approval for the niche MTC indication in the EU. Europe doesn't have any approved drugs for the advanced MTC cases the drug aims to treat, and outcomes for patients with the cancers have not improved much over the past two decades, according to AstraZeneca.

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