NEW YORK ( TheStreet) -- Shares of Onyx Pharmaceuticals ( ONXX) tanked 7.2% to $115.34 on concerns that Amgen's ( AMGN) interest in the biopharmaceutical company might have waned. Last week, Onyx said multiple parties remain interested in acquiring the cancer drug developer, but the public nature of the deal talks have raised doubts about the outcome. Onyx said June 30 that it received interest from Amgen at $120 per share, which the company rejected. In early August, media reports suggested Amgen was offering $130 per share. Now Bloomberg has reported that Amgen has agreed on the $130 price but conditioned upon reviewing data on Onyx's Kyprolis proteasome inhibitor, which is in accelerated approval with the Food and Drug Administration. Phase 3 trial results for the multiple myeloma treatment are expected by early 2014. Amgen said the reports that it was seeking information on Kyprolis did not originate from Amgen. Onyx declined to comment except to reiterate that multiple parties remain interested in a potential deal. The major concern seems to be that the Onyx auction is not as robust as initially expected, with hopes of a price topping $150 per share for the company. The public nature of the negotiation suggests that Onyx does not have as much active interest as the company expected. The odd element to the reports is the notion that Amgen is looking for additional data on Kyprolis application that is not yet available. Amgen did not have the data when it pitched its $120 offer in late June or when the bidder apparently raised to $130 earlier this month. Interim data on Kyprolis is not important enough to derail a deal with Amgen, a sell-side analyst said. An interim look is neither crucial nor definitive, and the request for unavailable data is unreasonable on the surface, the analyst said. It feels more like Amgen, if the story is accurate, does not think it faces competition in the auction, the analyst said. But the availability of an interim update on Kyprolis is not worth screwing up a deal over $10 per share, the analyst said.
-- Written by Scott Stuart in New York