A class of drugs is emerging that can attack cancer cells in the body without damaging surrounding healthy ones. They have the potential to replace chemotherapy and its disruptive side effects, reshaping the future of cancer care.

The complex biological medicines, called antibody drug conjugates (ADCs), have been in development for decades, and are now generating renewed excitement because of the success of one ADC in late-stage testing, a breast cancer treatment called DS-8201.

The fervor over ADCs is such that AstraZeneca PLC in March agreed to pay as much as $6.9 billion to jointly develop DS-8201 with Daiichi Sankyo Co., the British drugmaker's biggest deal in more than a decade. The investment was widely seen to be a validation of DS-8201's potential — and the ADC class of drugs as a whole — as an alternative to chemotherapy, the most widely used treatment, for some types of cancer.