iStock,
Dilok Klaisataporn
At the European Society for Medical Oncology meeting this weekend, Merck will showcase three late-stage trials of its Kelun-Biotech–partnered TROP2-directed antibody sac-TMT that VP of Chemistry Alan Northrup says gets the payload release “just right.”
Twelve years ago, Merck won FDA approval for the PD-1 inhibitor Keytruda, heralding a
new era
of cancer treatment—and opening the door to billions of dollars in revenue. Now, with immuno-oncology seemingly on the verge of its
next breakthrough
, Merck is looking to stake a new claim on the market—this time in the growing space of antibody-drug conjugates.
While the antibody-drug conjugate (ADC) market is crowded with candidates, Merck Vice President of Chemistry Alan Northrup believes the company’s Kelun-Biotech–partnered TROP2 ADC is “just right.”
ADCs, which marry the targeting properties of antibodies with the cancer-killing capabilities of cytotoxic drugs such as chemotherapy in hopes of effectively destroying tumor cells while sparing the healthy ones, “remain one of oncology’s most attractive modalities,” Truist Securities said in an Oct. 12 note to investors, “but a crowded pipeline raises the bar for differentiation.”
H.C. Wainwright agreed, writing in a Sept. 28 Deep Dive on the space that “the ADC boom could reshape oncology, defend Merck’s $30B+ [Keytruda] franchise, and reward drugs that overcome resistance or keep patients on therapy.” Sac-TMT, specifically, “could preserve Merck’s central role in frontline oncology beyond Keytruda’s December 2028 primary U.S. patent expiration,” the analysts continued. They added that replacing conventional chemotherapy with ADCs while retaining Keytruda in treatment regimens could address the same large opportunity pursued by PD-(L)1/VEGF bispecific antibodies, which Vision Lifesciences
projects
will be worth $30 billion by 2032.
Merck’s
pipeline
currently includes six ADCs, a company representative confirmed, including the B7-H3 directed ifinatamab deruxtecan (I-DXd), the Nectin-4-directed MK-3120 and the Daiichi Sankyo–partnered patritumab deruxtecan. The subject of most attention, however, is Merck and Kelun’s sacituzumab tirumotecan (sac-TMT), a TROP-2-targeted ADC in development for a range of indications, including bladder, breast, cervical and endometrial cancer.
The Goldilocks zone
TROP2-directed ADCs are fairly new to the market. The first such drug—Gilead Sciences’ Trodelvy—was greenlit by the FDA in April 2020 for patients with metastatic triple-negative breast cancer. Three years later, AstraZeneca and Daiichi Sankyo’s Datroway was approved for the same disease.
Northrup explained that most ADCs—including Trodelvy and Datroway—have a reversible payload linkage to the antibody, while sac-TMT has an irreversible linkage, which keeps the drug stable in the blood until it reaches the tumor.
“You’re trying to find that Goldilocks zone,” he told
BioSpace
. Some linker payloads are “too hot,” so the payload is released throughout the body, and some are “too cold,” meaning their release is slow once they hit the tumor. “[Sac-TMT] is right in that middle zone where it’s just right.”
This is key to successful treatment, Northrup explained, because when a payload is released early, it is free to circulate through the body, causing myriad issues, including anemia and neutropenia—a condition in which the body has an unusually low number of neutrophils, which attack bacteria and other invaders. Merck believes these adverse effects are due to free payload. On the other hand, if payload release is delayed too long, “you may have also hit a lot of the on-target tissues as well, where TROP2 is expressed in other parts of the body.”
The irreversible linker was part of what drew Merck to Kelun nearly four years ago when the New Jersey giant committed
upwards of $9.4 billion biobucks
in December 2022 to work with the China-based biotech on seven ADC candidates for cancer targets.
“When we first met with Kelun and started talking with them about their technology, I think we were really impressed by this bifunctional linker because it was really unique in the field,” Northrup said. Merck was watching the development of Datroway and Trodelvy, “and we saw this as something that would be very unique in the field and would get it just right.”
So, is the proof in the proverbial porridge? “I think the trials speak for themselves,” Northrup said.
Sac-TMT will be featured in three late-breaking sessions at the
2026 European Society for Medical Oncology (ESMO) Congress
, which begins Friday in Madrid.
Sac-TMT’s clinical program
One of Merck’s ESMO late-breakers will feature the
Phase 3 OptiTROP-Lung06 trial
in non-small cell lung cancer (NSCLC). In results that read out in July, sac-TMT plus Keytruda meaningfully improved progression-free survival (PFS) vs. the first-line standard of care (immunotherapy plus chemotherapy), meeting the trial’s primary endpoint. The result established another breakthrough, according to Leerink Partners at the time: The first direct proof-of-concept for an ADC that could replace standard of care platinum-based chemo for first-line NSCLC.
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It was also the first Phase 3 trial of an ADC combined with a checkpoint inhibitor to meet its primary endpoint in first-line driver gene–negative and PD‑L1–negative non-squamous NSCLC, Kelun said in its July 14
press release
.
RBC analysts at the time called the trial success “another positive for Merck’s sac-TMT franchise” as it extends the sac-TMT/Keytruda combo from the PD-L1-positive population into the more challenging PD-L1-negative segment.
Meanwhile, in their Oct. 12 note, Truist analysts said that “Sac-TMT and [Datroway] establish key efficacy and safety reference points for next-wave ADCs, with TROP2 remaining the most clinically advanced target.”
In the same slot on Sunday, Kelun and Merck will discuss final overall survival (OS) data from the Phase 3 OptiTROP-Lung04 trial, which pitted sac-TMT against platinum chemotherapy in EGFR-mutated NSCLC after progression on a treatment that blocks the EGFR tyrosine kinase domain. The risk of disease progression or death was 51% lower for patients taking the ADC, which met the trial’s primary endpoint, Kelun
reported
in October 2025. OS was a key secondary endpoint of the trial.
And on Monday, sac-TMT’s
successful Phase 3 TroFuse-005 trial
in advanced endometrial cancer will be showcased in the Presidential Symposium. In May, the partners reported that TroFuse-005 hit its primary endpoint at an interim analysis, demonstrating significantly better OS and PFS compared to chemo in patients who had undergone prior treatment with platinum-based and anti-PD-1 therapies. The companies promised to provide more details at an upcoming medical congress, which was expected to be ESMO.
It hasn’t all been smooth sailing for Merck’s ADC pipeline, though. The pharma and partner Daiichi Sankyo
withdrew an application
for accelerated approval of I-DXd in extensive-stage small cell lung cancer after the FDA found that the companies’ data package did not meet the criteria.
“As a field, we can always continue to get better at delivering precisely to the tumor,” Northrup said when asked whether there is a limit to what ADCs can do. He provided two ways in which this can be done: more specific targeting and a more efficacious linker payload, “making sure that you can hold tight to the antibody and release where you want to in the tumor.
“I think Sac-TMT does that very well.”
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