FDA Denies Approval for Merck-Daiichi Lung Cancer Drug

The U.S. FDA has issued a complete response letter (CRL) regarding the Biologics License Application (BLA) for patritumab deruxtecan (HER3-DXd), an antibody-drug conjugate (ADC) developed jointly by Daiichi Sankyo and Merck & Co. The companies sought expedited approval for the treatment of adult patients with locally advanced or metastatic EGFR-mutated non-small cell lung cancer (NSCLC) who have previously undergone two or more systemic therapies. The CRL was primarily due to issues found during the inspection of a third-party manufacturing facility, although no concerns were raised about the drug's efficacy or safety.

Patritumab deruxtecan is designed as a HER3-directed DXd ADC aimed at treating EGFR-mutated NSCLC. It was developed using Daiichi Sankyo’s proprietary DXd ADC technology. Clinical trials have shown encouraging results, including the HERTHENA-Lung01 phase 2 trial, which recorded an objective response rate (ORR) of 29.8% in 225 patients with advanced NSCLC. The median duration of response in these patients was 6.4 months. The safety profile observed in this trial was consistent with earlier phase 1 trials, which supports the drug’s potential as a treatment option. The primary endpoint of the trial was ORR, while secondary endpoints included duration of response, progression-free survival, and overall survival.

In 2023, Merck entered into a significant financial agreement with Daiichi Sankyo, paying $4 billion upfront and an additional $1.5 billion in continuation payments, with potential further payments up to $16.5 billion. This agreement is part of a broader initiative to co-develop and potentially commercialize three ADC candidates worldwide (excluding Japan): patritumab deruxtecan (HER3-DXd), ifinatamab deruxtecan (I-DXd), and raludotatug deruxtecan (R-DXd). Among these, ifinatamab deruxtecan is currently being evaluated as a monotherapy for small cell lung cancer, while raludotatug deruxtecan is in a phase 1 clinical trial for advanced ovarian cancer.

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