Astrazeneca plc, faced with what CEO Pascal Soriot recently called "probably the largest patent expiry in the industry as a proportion of the total company," has agreed to pay Daiichi Sankyo Co. Ltd. up to $6.9 billion to jointly develop and commercialize an antibody-drug conjugate (ADC) for the potential treatment of multiple HER2-expressing cancers. The deal for trastuzumab deruxtecan (DS-8201), which could have big benefits for both companies, includes $1.35 billion up front for Daiichi Sankyo. It could also yield a further $5.55 billion in milestone payments to the Tokyo-based big pharma.