By Ben Hirschler and Leigh Thomas LONDON/PARIS (Reuters) – French drugmaker Sanofi went public with a $9.3 billion offer to buy Medivation on Thursday, setting up what could be a lengthy takeover fight after the U.S. cancer firm rebuffed its approaches. The decision to target Medivation marks a return to the biotech takeover trail for Sanofi, which is looking to new cancer treatments to bolster its portfolio and help offset declining sales of mainstay diabetes drug Lantus. Sanofi’s non-binding proposal is to buy Medivation for $52.50 per share in cash, representing a 50 percent premium over the San Francisco-based firm’s two-month volume-weighted average share price prior to takeover rumors.