Thousand Oaks-based biotech giant Amgen said Monday afternoon that it is acquiring Biovex, a Woburn, Massachusetts-based developer of treatments for melanoma and head and neck cancer. Amgen said it will pay up to $1 billion for the company, including $425M in cash at closing and up to $575M in earn out based on regulatory and sales milestones. BioVex develops OncoVEX, a novel oncolytic vaccine in Phase 3 clinical development. The firm was venture backed by Morningside Venture Investments, MVM Life Science Partners, Sectoral Asset Management, Ventech, and Ysios Capital Partners.