Merck has built a bullish view on sacituzumab tirumotecan across multiple cancer types based on promising data from other TROP2 antibody-drug conjugates and from its partner Kelun-Biotech in China.\n Oct. 14, days before the 2025 European Society for Medical Oncology (ESMO) Congress in Berlin, Merck & Co. published a new clinical trial of sacituzumab tirumotecan (sac-TMT), in combination with the company’s PD-1 inhibitor Keytruda, as a first-line maintenance treatment for patients with cervical cancer. The TroFuse-036 study marked the 15th global phase 3 that the New Jersey pharma has launched for the TROP2 antibody-drug conjugate, licensed from China’s Kelun-Biotech, in the span of about three years.Meanwhile, detailed results from the phase 3 Leap-014 trial released at ESMO 2025 served as a poignant reminder of the disappointing outcomes the last time Merck went so aggressive on a cancer drug program.The Leap-014 trial, conducted in untreated patients with metastatic esophageal squamous cell carcinoma, missed its primary endpoint of overall survival (OS). Compared with Keytruda and chemo, Merck’s Eisai-partnered Lenvima—used in tandem with Keytruda and chemo—only showed an 8% reduction in the risk of death, which was not statistically significant. Patients in the experimental arm lived a median 17.6 months, versus 15.5 months for those in the control arm.As OS was not positive, the secondary endpoint of progression-free survival (PFS) was not tested for statistical significance. Data there were not promising, either, as the Lenvima-based regimen only reduced patients’ risk of progression or death by 11%.Leap-014 joins eight other phase 3 Leap trials in the failure category. Elsewhere, Leap-012 and Leap-015 have met on PFS but not OS, raising a degree of uncertainty about Merck and Eisai’s plans and whether regulators will be persuaded if the data are eventually submitted.But Marjorie Green, M.D., Merck’s senior vice president and head of oncology global clinical development, remained bullish on sac-TMT.“I anticipate, across multiple tumor types and multiple indications, this is a workhorse drug,” Green said about sac-TMT in an interview with Fierce Pharma.Green built her optimism on promising data from other TROP2 ADCs and from Merck’s partner Kelun in China.“This is not the only TROP2 ADC out there. There are data sets from other companies,” Green said in an interview with Fierce Pharma. “The drugs are not identical—they have different therapeutic indexes—but there is a lot of data out there that supports the indications where we’ve moved sac-TMT.”Lenvima and sac-TMT address different biological questions, she added. While Lenvima is an anti-angiogenic drug, Green described sac-TMT as a targeted chemotherapy of a topoisomerase inhibitor.“We know that topoisomerase inhibitors are effective across all the tumor types where we have studies ongoing,” Green said. “And with the use of an antibody-drug conjugate, you’re able to get a more potent payload and improve the efficacy.”The large data sets Kelun has accumulated in China—some of which have not been publicly presented—offered a “significant amount of information that helped us to ungate these studies.”At ESMO 2025, Kelun detailed two recent positive Chinese phase 3 trials, offering a glimpse into what sac-TMT might one day achieve in its counterpart global studies. A unique EGFR lung cancer winIn patients with tyrosine kinase inhibitor-pretreated EGFR-mutant non-small cell lung cancer, sac-TMT significantly lowered the risk of death by 40% versus chemotherapy, according to results from a preplanned interim analysis of the OptiTROP-Lung04 trial. Median OS was not reached in the sac-TMT arm compared with a result of 17.4 months in the chemo group.Benefits were observed across subgroups analyzed, including in both those who had received a third-generation EGFR TKI in the first line and those who had one in the second line, as well as in patients with or without brain metastases and across EGFR mutation types. A small number of patients, 5.6% of the total randomized, had not received a prior third-gen TKI. The subgroup analysis does not include comparisons by TROP2 expression levels.Sac-TMT’s PFS benefit was also statistically significant, reaching 51% versus chemo by blinded central review, with a median PFS of 8.3 months versus 4.3 months, respectively.Sac-TMT achieved the OS showing even as 85.5% of patients in the chemotherapy arm received any subsequent treatment, including 19.6% who got an ADC. That’s compared to 72.3% of patients in the sac-TMT arm who got a follow-on therapy, including 1.4% for an ADC. In terms of safety, grade 3 or above treatment-related adverse events (TRAEs) were similar for sac-TMT and chemo, at 58% and 53%, respectively. Serious TRAEs were less frequent, at 9%, for sac-TMT, whereas the chemo group logged 17.6%.One important side effect of interest for sac-TMT is stomatitis, which is inflammation of the mucous membrane of the mouth, which can lead to painful oral ulcers. While not lethal, the problem can affect patients’ quality of life. The rate of any treatment-emergent stomatitis was 64%—including 5% at grade 3 with no more serious events—for sac-TMT, versus 5% in the chemo group, according to results published in The New England Journal of Medicine. The problem led to a 10.1% rate of dose reductions for sac-TMT but no discontinuations.Based on the results, Chinese authorities have already approved sac-TMT as a second-line treatment for EGFR-mutant NSCLC, Kelun announced Oct. 11.Besides the OS benefit, sac-TMT also comes with the advantage of being a single agent, while other regimens in this disease setting are combinations, the OptiTROP-Lung04 study investigators noted in the NEJM article. For example, in the HARMONi-A trial, which Akeso recently said also met its OS endpoint at the final analysis, the company’s PD-1xVEGF bispecific was used in combination with chemotherapy. Similarly, Johnson & Johnson’s FDA-approved antibody Rybrevant is also used together with chemo in second-line EGFR-mutant NSCLC.“I anticipate, across multiple tumor types and multiple indications, this is a workhorse drug.” — Marjorie Green, M.D., Merck’s senior vice president and head of oncology global clinical developmentIn an Oct. 20 note to clients, Leerink Partners analysts said OptiTROP-Lung04 offered “exemplary outcomes” which support Merck and Kelun’s ambitions in the EGFR-mutant NSCLC indication.For its part, Merck is currently trying to replicate the China-only success in the global TroFuse-009 and TroFuse-004 trials.Green acknowledged that the global trials will be conducted under more diverse practices than the China-only study. EGFR-mutant NSCLC is more common in China than in Western populations, and doctors have gotten very good at treating the disease in the country, she said. In China, Kelun evaluated sac-TMT at a 5mg/kg dose, while Merck has selected 4mg/kg for the two global registrational trials, Leerink analysts noted. With the dose reduction, the team said it would expect “somewhat worse efficacy outcomes but an improved safety profile.”In TROP2 for second-line EGFR-mutant NSCLC, Merck is racing against AstraZeneca, whose Daiichi Sankyo-partnered Datroway is being paired with the British pharma’s Tagrisso in the Tropion-Lung15 trial, with a readout expected in the second half of 2026. HR-positive, HER2-negative breast cancer resultsIn the second positive phase 3 Kelun reported at ESMO 2025, sac-TMT significantly reduced the risk of progression or death by a massive 65% versus chemo in patients with previously treated HR-positive, HER2-negative breast cancer, according to results by blinded central review from the OptiTROP-Breast02 trial.The ADC more than doubled patients’ median PFS to 8.3 months, versus 4.1 months for chemo.The results were consistent across subgroups, including in those who were HER2 nil (effect size 61%) and HER2-low (69%), as well as in those who received one line of chemo in the advanced stage (65%) or more than one (63%). Patients in the study had all tried endocrine therapy, plus a CDK4/6 inhibitor and chemo.While OS data were not mature after a median follow-up of 7.4 months, data strongly favored sac-TMT with a preliminary 67% reduction in the risk of death. The incidence of grade 3 or above TRAEs was similar between the two groups, at 62% for sac-TMT and 64.8% for chemo. Stomatitis again stood out for sac-TMT with a 63% rate of any grade, versus 8% for chemo. The stomatitis cases were generally mild and manageable, Man Li from the Second Affiliated Hospital of Dalian Medical University said during her presentation of OptiTROP-Breast02.In previously treated HR+/HER2- breast cancer, AZ and Daiichi’s Datroway already won an FDA approval in January. Sac-TMT’s performance appears favorable to Datroway’s by cross-trial comparison.In Tropion-Breast01, Datroway reduced the risk of disease progression or death by 37% versus chemo. The median PFS was 6.9 months and 4.9 months for the two arms, respectively.The trial, however, did not meet its other dual primary endpoint, OS, with a hazard ratio of 1.01. Even after accounting for subsequent ADC use, the adjusted hazard ratio was 0.86, equating a 14% death risk reduction in favor of Datroway. The comparison should be viewed with caution, as the two trials populations are not identical, including their proportions of second-line and third-line patients.Again hoping to expand sac-TMT’s win in HR+/HER2- breast cancer to a global population, Merck is running the TroFuse-010 trial, testing the drug either by itself or in combination with Keytruda in patients who have not tried chemotherapy in the advanced stage.Competition there includes Gilead Sciences’ Ascent-07 trial for Trodelvy.Editor\'s Note: The story was updated Oct. 21 at 8 a.m. ET to include additional comments from a Leerink Partners note.