On December 18, 2025 Daiichi Sankyo and Merck & Co. reported that phase 3 program for their investigational antibody-drug conjugate has been hit with a hold after an unexpected number of deaths were reported in the global trial.
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"Due to a higher than anticipated incidence of grade 5 interstitial lung disease (ILD) events identified in the IDeate-Lung02 phase 3 trial, Daiichi Sankyo initiated a voluntary pause in recruitment and enrollment," a spokesperson for the partners told Fierce Biotech. The companies did not answer questions regarding how many deaths have occurred.
"Following the initial pause, the FDA has placed the trial on a partial clinical hold," the spokesperson explained.
The unexpected deaths come as the pharma partners said they were aiming for an accelerated approval of the investigational B7-H3-directed ADC—known as ifinatamab deruxtecan or I-DXd—for pretreated small cell lung cancer (SCLC) based on a phase 2 readout. In 2023, Merck paid out $5.5 billion in upfront and near-term payments to gain access to a clutch of Daiichi’s ADCs.
Under the hold, Daiichi will work with the FDA and an independent data monitoring committee to review safety data and "determine any necessary further actions," the spokesperson told Fierce.
"Of note, it does not impact other studies in the I-DXd clinical development program," the spokesperson added.
Patients currently enrolled in IDeate-Lung02 will be able to continue treatment, but no new participants will be recruited during this time, according to the spokesperson.
"We are evaluating the potential impact of the partial clinical hold on study data readout timing, currently projected for fiscal year 2027," the spokesperson said.
The deaths and consequential hold have not been announced publicly by either Merck or Daiichi, but instead were first reported by oncology-focused publication ApexOnco. The temporary halts began in several European countries—such as France, Germany and Italy—at the end of September, according to the European clinical trial registry.
(Press release, FierceBiotech, DEC 18, 2025, https://www.fiercebiotech.com/biotech/patient-deaths-prompt-partial-hold-daiichi-mercks-global-phase-3-adc-program [SID1234661552])