It seems US regulators have not been wholly bowled over by data supporting the use of Pfizer's Sutent and Novartis' Afinitor as treatments for a rare type of pancreatic cancer.

Both companies are seeking to extend the labels of their drugs, which are on the market for other indications, to include the treatment of pancreatic neuroendrocrine tumours (NET), but documents posted on the US Food and Drug Administration's website have thrown a small shadow of doubt on whether their applications will be successful.

Clinical data filed with the regulator indicates that both Sutent (sunitinib) and Afinitor (everolimus) significantly improved progression-free survival for patients with pancreatic NET compared with a placebo.

But as Pfizer decided to stop its trial early, i.e. before the pre-specified efficiency goal was met, there is a risk that Sutent's effectiveness might have been over-estimated, meaning that the magnitude of its effect in pancreatic NET is uncertain, the reviewers note.

And with regard to Afinitor, there was concern over discrepancies in the benefit of the drug in two separate studies looking at different tumour origins.

Submission amended

Consequently, Novartis said it has amended its submission to only seek approval for the treatment of patients with advanced NET of pancreatic origin, instead of for patients with advanced NET of gastrointestinal, lung or pancreatic origin.

All eyes will now be on an FDA advisory panel which will meet on April 12 to discuss the clinical evidence for the use of Afinitor and Sutent in pancreatic NET.