Hollings C. Renton, Onyx Pharmaceuticals’ chief executive officer, announced plans to retire next year. Mr. Renton will remain chairman of the board of directors. The company has initiated a search for a successor. The company has promoted Laura A. Brege to the newly created position of executive vice president and chief operating officer and Randy A. Kelley to senior vice president of sales and marketing.     “With Nexavar established as an effective and well tolerated anti-cance...