When Japanese pharmaceutical company Daiichi Sankyo discovered a groundbreaking cancer treatment, it turned to bigger Western drugmaker AstraZeneca to help commercialize the therapy that has the potential to replace chemotherapy.

Now that Enhertu — their breast cancer drug that is on track to generate over $10 billion annually — is a proven global success, Daiichi Sankyo does not want to share other future complex biological cancer treatments.

"A good drug brings solutions to business,” President Hiroyuki Okuzawa said in an interview. "Enhertu helped us raise our profile, attract world class talent and boosted our capability in oncology. We played an equal part and led some trials. We now have the ability and experience to do it all by ourselves.”