AstraZeneca's vandetanib has suffered a setback in the USA after regulators said they need more time to assess the drug as a treatment for non-operable locally advanced or metastatic medullary thyroid cancer (MTC).

The drugmaker said Friday that the US Food and Drug Administration had requested a risk evaluation and mitigation strategy for vandetanib, and following the subsequent submission by AstraZeneca has extended the review period for the drug by three months - until April 7 - to allow it enough time to consider the plan.

Back in December an FDA advisory board recommended the approval of vandetanib for this rare type of thyroid cancer on the back of data from the Phase III ZETA study, which involved 331 patients with advanced MTC and showed that treatment with AstraZeneca's drug significantly extended progression-free survival and demonstrated a 54% reduction in the rate of progression compared to placebo.

But the panel did note concerns on the vandetanib's dosage, primarily because of the high number of side effects observed in patients, and consequently voted unanimously in favour of a post-approval study to the medicine's effect at other doses.

MTC accounts for 4% of all thyroid cancers and it is estimated that more than 44,000 new cases of the latter will be diagnosed in the USA in 2010. If approved the drug is projected to bring in $71 million in sales in 2015, according to analysts surveyed by Bloomberg, which should help to fill some of the huge gap in sales AstraZeneca is facing in the coming years as the patents on its big earners Nexium (esomeprazole) and Seroquel (quetiapine) crumble. 

AstraZeneca's shares slipped around 1.2% on the London Stock Exchange following news of the delay.