Eli Lilly’s experimental lung cancer drug necitumumab has raised concerns with the FDA after trial data it suggested it could increase the chance of fatal blood clots, despite improving survival.

The drug was tested in both squamous and non-squamous non-small cell lung cancer (NSCLC). In the squamous arm, taking necitumumab with chemotherapy drugs gemcitabine and cisplatin increased survival by 1.6 months compared to gemcitabine and cisplatin alone.

However the incidence of thromboembolic events was 9% in the necitumumab group compared to 5% in the control group.

The trial in non-squamous NCSLC was ended early because of the number of deaths that could be attributed to blood clots – the incidence rate in this study was 11% compared to 6% in the control group.

The FDA published its review ahead of a meeting today where cancer experts will discuss whether to recommend the drug for approval. The US regulator is not obliged to follow the advice of such advisory panels, but almost always does.

Previously necitumumab has been a promising drug for Lilly, boosting its stock on news of trial successes.