Merck and Daiichi Sankyo's Lung Cancer Drug Shows Promise in Pivotal Trial

Merck and Daiichi Sankyo have reported encouraging results from a pivotal Phase II trial of their antibody-drug conjugate (ADC) ifinatamab deruxtecan (I-DXd) in patients with extensive-stage small cell lung cancer. The data, presented at the 2025 World Conference on Lung Cancer, demonstrate a significant response rate and could pave the way for accelerated approval.

Strong Efficacy Data in Phase II Trial

The IDeate-Lung01 study showed that I-DXd achieved a confirmed objective response rate (ORR) of 48.2% in the overall patient population. This includes three complete responses and 63 partial responses, with an additional 54 patients achieving stable disease.

When focusing on patients receiving I-DXd in the second-line setting, the ORR rose to an impressive 56.3%. Jefferies analysts described these results as "strong" and "impressive," noting that the inclusion of third-line patients may have slightly diluted the overall efficacy figures.

Potential for Accelerated Approval

The robust efficacy data, coupled with the recent breakthrough therapy designation from the FDA, suggests that I-DXd could be on track for accelerated approval in extensive-stage small cell lung cancer. This regulatory pathway has previously been utilized for other drugs in this indication, including Jazz Pharmaceuticals' Zepzelca and Amgen's Imdelltra.

Jefferies analysts believe that an accelerated approval for I-DXd is a "distinct possibility," given the FDA's demonstrated flexibility in this area and the strength of the Phase II data.

A Comeback for Merck and Daiichi Sankyo's ADC Partnership

The positive results for I-DXd represent a crucial win for Merck and Daiichi Sankyo's collaboration on ADCs. This partnership, initiated in October 2023 with a $4 billion upfront payment from Merck, has faced challenges in recent months.

In June 2024, another asset from the collaboration, patritumab deruxtecan, failed to secure FDA approval for non-small cell lung cancer due to manufacturing issues. The companies subsequently withdrew the application entirely in May 2025 after the drug failed to show significant overall survival improvements in a Phase III study.

The success of I-DXd in this pivotal trial may help to reinvigorate the partnership, which could be worth up to $22 billion for Daiichi Sankyo if all milestones are met. As the pharmaceutical industry continues to invest heavily in ADC technology, the performance of I-DXd will be closely watched by investors and competitors alike.