ADC Therapeutics Falls Sharply Following Patient Deaths in Drug Trial

• The treatment arm recorded 27 deaths (13.2%) versus 9 deaths (4.6%) in the control arm receiving Rituxan and chemotherapy, with most fatalities in patients 75 years or older
• Zynlonta received accelerated FDA approval in 2021, and this confirmatory study is crucial for full U.S. approval; ADC plans to meet with the FDA in August and submit a supplemental application in Q4 2024
• The company attributed higher deaths partly to the older patient population and longer monitoring in the treatment arm, though analysts noted most other treatments for this cancer have single-digit death rates

ADC Therapeutics Shares Plunge After Trial Deaths

ADC Therapeutics experienced a sharp stock decline following disappointing results from a confirmatory study of its cancer drug Zynlonta. The trial, which combined Zynlonta with Roche's Rituxan, revealed a significantly higher death rate compared to standard treatment.

Key Trial Data:

• Treatment arm (Zynlonta + Rituxan): 27 deaths (13.2%)
• Control arm (Rituxan + chemotherapy): 9 deaths (4.6%)
• Most treatment arm deaths occurred in patients aged 75 or older
• The trial involved patients with relapsed or refractory diffuse large B-cell lymphoma, an aggressive blood cancer

Clinical Context:

Zynlonta, an antibody-drug conjugate designed to target cancer cells while minimizing healthy tissue damage, received FDA accelerated approval in 2021. This confirmatory study was critical for securing full U.S. approval. Despite favorable results on other efficacy endpoints, the elevated mortality rate overshadowed the drug's benefits.

ADC Therapeutics attributed the higher death rate to the older patient population and longer adverse event monitoring, noting that treatment arm patients stayed on therapy longer while control patients often switched to alternative treatments early.

Market Implications:

Guggenheim analyst Michael Schmidt noted that while most DLBCL treatments report single-digit death rates, the company's value proposition as a "community-friendly" alternative to bispecific antibodies will likely face investor scrutiny. ADC plans to meet with the FDA in August and submit a supplemental application in Q4 2024, though the path to full approval now appears uncertain given the safety concerns.