June 4 (Reuters) – ADC Therapeutics shares slumped nearly 53% in premarket trading on Thursday after a late-stage study testing its blood cancer drug showed more deaths among treated patients, despite meeting its main goal of improving progression-free survival.
The confirmatory study tested ADC’s Zynlonta along with Roche’s monoclonal antibody Rituxan in patients with relapsed or refractory diffuse large B-cell lymphoma, an aggressive, fast-growing blood cancer that affects the lymphatic system.
There were 27, or 13.2%, deaths in the treatment arm, compared with 9, or 4.6%, deaths in the control arm, which received Rituxan and chemotherapy, the company said late on Wednesday. Most deaths in the treatment arm occurred in patients aged 75 years or older, it added.
While other efficacy endpoints looked favorable, the result was overshadowed by a higher rate of deaths in the Zynlonta arm, Guggenheim analyst Michael Schmidt said.
Zynlonta was granted an accelerated approval by the U.S. Food and Drug Administration in 2021 and the confirmatory study was crucial to show its clinical benefits for full approval in the U.S.
ADC said it plans to meet with the FDA in August and submit a supplemental application in the fourth quarter this year.
“The overall value proposition of the combination — which is targeted as a community-friendly & easy-to-administer therapy for patients that are not bispecific antibody candidates — will likely be debated by some investors,” Schmidt said.
Zynlonta is an antibody-drug conjugate designed to precisely target cancer cells, while limiting damage to healthy tissue.
The company attributed the higher death rate in part to the older patient population and longer adverse event monitoring in the treatment arm, where patients stayed on therapy longer as control-arm patients often switched early to other treatments.
“While Grade 5 TEAEs (deaths) are generally unfortunately not uncommon in the treatment of DLBCL, most other regimens have single-digit percentage Gr 5 TEAE rates, with higher rates reported due to COVID-19 during the pandemic,” Schmidt said.
(Reporting by Mariam Sunny in Bengaluru; Editing by Joyjeet Das)
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