By Karlee Weinmann (August 23, 2013, 1:24 PM EDT) -- California drugmaker Amgen Inc. wants to pay less than the $9.5 billion buyout offer it made earlier this month for Onyx Pharmaceuticals Inc. after the target company held back on distributing clinical trial data for a highly touted cancer treatment plodding toward regulatory approval in the U.S. and Europe, according to a Friday report from Bloomberg. Some reports have indicated that Onyx bowed to Amgen pressure to release the data, which it had feared could violate patient privacy and disrupt the approval process for its latest drug, Kyprolis. But without complete information, Amgen has said it cannot accurately place a value on the drug — or Onyx....