In a potential US$251 M deal, Exelixis has granted Merck & Co. worldwide rights to its preclinical PI3K-delta R&D programme, including XL499, the programme’s lead compound that has potential in the treatment of rheumatoid arthritis, allergic asthma and haematological malignancies. Merck will be solely responsible for the research, development and commercialisation of compounds originating from the programme. The agreement will provide Exelixis with resources to continue the development of its most advanced compound, cabozantinib, which is in Phase III development for medullary thyroid cancer.