ADC Therapeutics disclosed that its antibody-drug conjugate Zynlonta hit a stumbling block after confirmatory phase 3 results in relapsed or refractory diffuse large B-cell lymphoma. The LOTIS-5 trial met its primary progression-free survival endpoint, but overall patient deaths were higher in the treatment arm than in rituximab monotherapy. The company said fatalities tied to treatment-emergent adverse events were three times higher in the Zynlonta arm, with infections cited as a leading cause. ADC also reported that overall survival showed no detrimental effect on its key secondary measures, but the death imbalance is expected to weigh on regulatory and market discussions. Investors will likely scrutinize how the adverse-event pattern compares with prior Zynlonta studies and whether trial conduct elements, such as observation and switching windows, can be reconciled with the safety signal.