Trial data reportedly holding up Amgen's plans to acquire Onyx

SOUTH SAN FRANCISCO—Those "unnamed sources" who are "close to the deal" are speaking to various media outlets again about the potential acquisition of Onyx Pharmaceuticals Inc. by Amgen Inc. And this time, they say a deal is close, but that Onyx's unwillingness to give over clinical trial data for European approval of Kyprolis is what's hanging things up.

At the crux of the matter is that Onyx doesn't have data for the blood-cancer treatment because the trial is still in process, but Amgen wants to see where things are at so that it can better gauge the potential future market value of Kyprolis. Onyx doesn't want to ask for early data out, though, reportedly out of concern that doing so might cause delays in future approval of the drug.

Data from the trial aren't due to come out until the first half of 2014.

Although talks of the acquisition are said to have "stalled" over this issue, the inside sources do indicate that Onyx is agreeable to a current offer of $130 per share, which would make for a roughly $9.5 billion deal. That's a 50 percent premium, more or less, over where Onyx's shares were selling for when news of a potential acquisition became public knowledge in late June.

Whether this sticking point will derail a deal remains to be seen, but Onyx already has a track record with some $362 million in2012 in revenue from Nexavar (for liver and kidney cancer) and Stivarga (for stomach cancer), both of which it is selling in partnership with Bayer AG

Analysts have estimated that revenue from Kyprolis could grow to $2.4billion by 2019.