AstraZeneca will pay Daiichi Sankyo $1.35 billion to jointly develop the antibody-drug conjugate trastuzumab deruxtecan. The ADC combines a HER2-targeting antibody with a topoisomerase I inhibitor, with the goal of delivering the powerful chemotherapy directly to cancer cells. The companies plan to file for regulatory approval of the drug, now in studies to treat people with HER2-expressing breast and gastric cancers, later this year. Daiichi, which will produce the drug, stands to rake in another $5.5 billion in sales and other milestone payments.