ADC Therapeutics shares plunge as Phase 3 trial of Zynlonta shows high death rate despite efficacy gain

ADC Therapeutics reported Phase 3 data for Zynlonta combined with rituximab in a hard-to-treat blood cancer. The trial met its primary endpoint by extending progression-free survival versus standard therapy.

However, the study also recorded a higher number of deaths among patients receiving the combination, raising safety concerns.

Analysts noted the mortality signal could be hard for physicians, patients and regulators to accept, especially since Zynlonta received accelerated approval in 2021 based on earlier data without a placebo comparator.

The negative safety perception drove ADC Therapeutics' shares down more than 50% in trading on Thursday.