The Federal Trade Commission has moved quickly to allow Amgen Inc. to proceed with its $10.4 billion acquisition of cancer drug maker Onyx Pharmaceuticals Inc. The FTC on Wednesday ended the waiting period required under federal antitrust laws before the acquisition could go forward. The period had been scheduled to end on Sept. 23. The Thousand Oaks biopharmaceutical company offered $125 a share on Aug. 25 for the South San Francisco firm, which has three primary commercial drugs: Kyprolis, a treatment for blood cancers; Nexavar, a drug for liver and kidney cancer; and Stivarga, a colon cancer drug. The offer was only a slight premium over a June 30 offer of $120 a share that the Onyx board rejected, saying it significantly undervalued the company. Amgen Chief Executive Robert Bradway has said the acquisition will accelerate his company’s growth and enhance shareholder value. In particular, the company plans to expand the global market for Kyprolis. The deal is expected to close by Oct. 1. Shares of Amgen lost 34 cents, or a fraction of a percent, to close at $117.18 on the Nasdaq.