In December 2014 the company received FDA approval for the use of the PD-1 inhibitor nivolumab (Opdivo) in treating patients whose skin cancer cannot be removed or have not responded to previous drug therapies. In February 2015, the company initiated a research partnership with Rigel Pharmaceuticals which could generate more than $339 million. In March, the company obtained an exclusive opportunity to both licence and commercialise PROSTVAC, Bavarian Nordic's phase III prostate specific antigen targeting cancer immunotherapy. Bavarian Nordic would receive an upfront payment of $60 million as well as incremental payments up to $230 million, if the overall survival of test patients exceeds that seen in Phase II tests. Bavarian could also receive milestone payments of between $110 million and $495 million, dependent on regulatory authorization, and these payments have the potential to total up to $975 million.