PARIS, May 12 (Reuters) - U.S. pharmaceutical and healthcare giant Pfizer announced on Sunday a 500 million-euro ($538 million) investment in France for research and development, ahead of the start of this year's annual 'Choose France' business summit. ($1 = 0.9286 euros) (Reporting by Sudip Kar-Gupta and Elizabeth Pineau; Editing by Hugh Lawson)