Antibody-drug conjugates (ADCs) have become one of the fastest-growing classes of cancer therapy over the past decade, combining the tumour-targeting precision of a monoclonal antibody with the cell-killing power of a cytotoxic payload. Sacituzumab tirumotecan — known in the clinical literature by its development codes MK-2870 and SKB264, and abbreviated sac-TMT — is one of the more clinically advanced molecules in this category, with an active global trial programme spanning breast, lung, urothelial, gastroesophageal, and head and neck cancers.

This article summarises what is publicly known about sac-TMT's design, clinical trial data, safety profile, and regulatory status, based on peer-reviewed literature, clinical trial registries, and public regulatory announcements. It is intended purely as an educational reference for healthcare professionals and informed readers and does not promote the use of this or any product.

What Is Sacituzumab Tirumotecan?

Sac-TMT is a TROP2-directed antibody-drug conjugate. TROP2 (trophoblast cell-surface antigen 2) is a transmembrane glycoprotein that is overexpressed on the surface of many epithelial tumour cells — including triple-negative breast cancer, hormone receptor-positive breast cancer, non-small cell lung cancer (NSCLC), and urothelial carcinoma — while being expressed at much lower levels on normal tissue. This differential expression makes TROP2 an attractive target for selectively delivering cytotoxic chemotherapy to tumour cells while limiting systemic exposure.

Structurally, sac-TMT is composed of three parts:

1. A humanised monoclonal antibody that binds TROP2
2. A proprietary bifunctional linker — a pyrimidine-thiol ("Kthiol") linker designed to be stable in circulation but cleavable in the tumour microenvironment
3. A cytotoxic payload — a belotecan-derived topoisomerase I inhibitor, conjugated at a mean drug-to-antibody ratio (DAR) of approximately 7.4

Upon binding TROP2 on the tumour cell surface, the ADC is internalised and the payload is released — through pH-sensitive cleavage in the tumour microenvironment or enzymatic hydrolysis inside the cell — where it inhibits topoisomerase I, causing DNA damage and cell death. Because the released payload can also diffuse to neighbouring tumour cells regardless of their individual TROP2 expression level (a "bystander effect"), the drug is designed to be active even in tumours with heterogeneous target expression.^[1,2]

It is worth noting for scientific accuracy that sac-TMT shares its underlying anti-TROP2 antibody with another, already-marketed TROP2-directed ADC — but the two molecules differ meaningfully in their linker chemistry (pyrimidine-based versus maleimide-based) and their cytotoxic payload, which is a key reason their clinical profiles are evaluated as distinct molecules rather than interchangeable products.^[3]

Clinical Development Programme

Sac-TMT is being developed through an extensive, multi-indication clinical programme, originated by Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd., with global co-development and commercialisation (outside Greater China) led by Merck & Co. (known as MSD outside the United States and Canada) under a licensing collaboration. As of early 2026, more than a dozen Phase 2 and Phase 3 trials were active across breast cancer, lung cancer, urothelial carcinoma, gastroesophageal adenocarcinoma, and head and neck squamous cell carcinoma, in addition to the original Phase 1/2 dose-finding study (NCT04152499), which enrolled over 1,400 patients globally.^[2,4]

The trial programme is organised under two umbrella names depending on tumour type: "OptiTROP" studies (led primarily by Kelun-Biotech in China) and "TroFuse" studies (Merck/MSD-sponsored global registrational trials).

Efficacy Data by Tumour Type

Triple-Negative Breast Cancer (TNBC)

The pivotal Phase 3 OptiTROP-Breast01 trial (NCT05347134) compared sac-TMT monotherapy against physician's choice of chemotherapy (eribulin, capecitabine, gemcitabine, or vinorelbine) in patients with previously treated, locally recurrent or metastatic TNBC who had received two or more prior systemic therapies. At final analysis, median progression-free survival (PFS) by blinded independent central review was 6.7 months with sac-TMT versus 2.5 months with chemotherapy (hazard ratio 0.32), representing a substantial reduction in the risk of progression or death.^[5]

HR-Positive, HER2-Negative Breast Cancer

The Phase 3 OptiTROP-Breast02 trial evaluated sac-TMT against investigator's choice of chemotherapy in patients with previously treated hormone receptor-positive, HER2-negative metastatic breast cancer. Reported results showed sac-TMT reduced the risk of disease progression or death by approximately 65% compared with chemotherapy, with a positive trend also observed for overall survival. This data supported the drug's fourth approved indication in China.^[6,7]

EGFR-Mutated Non-Small Cell Lung Cancer

Two separate Phase 3 trials have examined sac-TMT in EGFR-mutated NSCLC that has progressed after targeted therapy:

• OptiTROP-Lung03 compared sac-TMT with docetaxel in patients previously treated with an EGFR tyrosine kinase inhibitor (TKI) and platinum-based chemotherapy, demonstrating significantly improved objective response rate, PFS, and overall survival, alongside a lower rate of grade ≥3 treatment-related adverse events than docetaxel (56% vs 72%).^[8,9]
• OptiTROP-Lung04, published in the New England Journal of Medicine, compared sac-TMT monotherapy with pemetrexed plus platinum-based chemotherapy in 376 patients whose disease had progressed after EGFR-TKI therapy. Median PFS was 8.3 months with sac-TMT versus 4.3 months with chemotherapy (hazard ratio 0.49), with the trial also reporting a statistically significant overall survival benefit.^[10,11]

PD-L1-Positive NSCLC (Combination with Immunotherapy)

The Phase 3 OptiTROP-Lung05 trial (NCT06448312) evaluated sac-TMT combined with the anti-PD-1 antibody pembrolizumab against pembrolizumab monotherapy as first-line treatment in PD-L1-positive advanced NSCLC without targetable genomic alterations. An interim analysis reported that the combination significantly prolonged PFS compared with pembrolizumab alone, along with a favourable trend in overall survival — reported as the first Phase 3 trial of an ADC combined with a checkpoint inhibitor to meet its primary endpoint in first-line NSCLC.^[12,13]

Other Tumour Types Under Investigation

Sac-TMT is also being studied in:

• Advanced/metastatic urothelial carcinoma — early cohort data from the Phase 1/2 study (2870-001/KL264-01) reported an objective response rate signal in patients previously treated with platinum chemotherapy and checkpoint inhibitors.^[14]
• Gastroesophageal adenocarcinoma (NCT06356311, Merck-sponsored, ongoing)
• Head and neck squamous cell carcinoma, in combination with the checkpoint inhibitor toripalimab, in an early-phase study reporting an objective response rate of 16%.^[15]
• Neoadjuvant and early-stage breast cancer, including a Phase 3 study (MK-2870-032) evaluating sac-TMT-based regimens before surgery in high-risk early TNBC and HR-low/HER2-negative breast cancer.^[16]

These studies remain investigational and their tumour types are not currently part of any approved indication.

Safety and Tolerability Profile

Across the clinical programme, the safety profile of sac-TMT has been broadly consistent with other ADCs carrying topoisomerase I inhibitor payloads. Reported adverse events include:

• Haematologic toxicities: neutropenia, leukopenia, and anaemia are the most consistently reported grade ≥3 adverse events across trials (for example, grade ≥3 neutropenia occurred in 43% of sac-TMT-treated patients versus 59% with docetaxel in OptiTROP-Lung03).^[9]
• Gastrointestinal effects: nausea (mostly grade 1–2) and stomatitis, which was more frequent with sac-TMT than with chemotherapy comparators in some trials but generally reported as low-grade and manageable with dose modification and supportive care.^[6,17]
• Alopecia, reported in roughly two-thirds of patients in early studies.^[17]
• Notably infrequent findings across the published data include low rates of febrile neutropenia (not observed in some trials, versus 20% with docetaxel in OptiTROP-Lung03) and a low reported incidence of ocular toxicity (2%) and interstitial lung disease (0% reported in the EGFR-mutant NSCLC trials) — both of which are watched closely for ADCs in this broader class.^[9]
• No treatment-related deaths have been reported in the major published trials to date.^[1,5,9]

Dosing across most trials has used sac-TMT at 5 mg/kg administered intravenously every two weeks, with some earlier-phase and combination studies using alternative schedules (e.g., every 3 weeks) or lower doses (4 mg/kg) in specific settings.^[3,17,18]

Regulatory Status

As of mid-2026, sac-TMT's regulatory status differs significantly by region.

China (NMPA)

Sac-TMT has received sequential marketing approvals from China's National Medical Products Administration for four distinct indications:

Approval	Date	Indication	Supporting Trial
1st	November 2024	Locally advanced/metastatic TNBC after ≥2 prior systemic therapies	OptiTROP-Breast01
2nd	March 2025	EGFR-mutant non-squamous NSCLC after EGFR-TKI + platinum chemotherapy	OptiTROP-Lung03
3rd	October 2025	EGFR-mutant non-squamous NSCLC after EGFR-TKI therapy	OptiTROP-Lung04
4th	February 2026	Unresectable/metastatic HR+/HER2- breast cancer after endocrine therapy + ≥1 chemotherapy line	OptiTROP-Breast02

Sac-TMT was reported as the first fully NMPA-approved, China-originated TROP2-directed ADC.^[19–22]

United States (FDA)

Sac-TMT is not yet approved by the U.S. Food and Drug Administration. In December 2024, the FDA granted Breakthrough Therapy Designation to sac-TMT for advanced or metastatic EGFR-mutated non-squamous NSCLC that has progressed after EGFR-TKI and platinum-based chemotherapy, based on Phase 2 data. This designation is intended to expedite the drug's development and regulatory review process; it is not a marketing approval and does not by itself indicate the drug is available for prescription in the U.S.^[23,24]

Global Development

Beyond China, sac-TMT is in Phase 3 development across multiple regions as part of a broad global registrational programme, sponsored by Merck (MSD), spanning breast cancer, NSCLC, and additional solid tumour indications. Outcomes and regulatory timelines for these studies have not been finalised as of this writing.^[4]

Understanding Patient Access Pathways During the Regulatory Approval Process

The gap in sac-TMT's regulatory status across regions — approved for multiple indications in China, still investigational elsewhere — is not unique to this molecule. It reflects a broader, well-documented reality in oncology: regulatory review is deliberately rigorous and therefore takes time, but for patients with a life-threatening cancer and no remaining standard-of-care options, that timeline can outpace their disease. This tension is a recognised challenge across the oncology field and is the reason several formal pathways exist to allow physician-directed access to investigational or not-yet-locally-approved medicines outside standard commercial channels.

The terminology differs by region, but the underlying mechanisms are well established and regulator-defined:

• Expanded Access ("Compassionate Use") — In the United States, the FDA's Expanded Access pathway allows a treating physician to request an investigational drug for a patient with a serious or immediately life-threatening condition when no comparable or satisfactory alternative therapy exists and the patient cannot enrol in a clinical trial. The FDA reports approving the large majority of such requests, and launched Project Facilitate in 2019 specifically to help oncology physicians navigate the process.^[25,26]
• Compassionate Use and Named Patient Use — The European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) distinguishes between "Compassionate Use" (for a cohort of patients, coordinated at a national level) and "Named Patient Use" (for an individual patient, requested by their physician), both intended for medicines that are not yet authorised but are needed for a serious or life-threatening condition.^[27]
• Managed Access / Named Patient Supply programmes — More broadly, terms such as Managed Access Program (MAP) or Named Patient Supply are used internationally to describe structured, physician-initiated, regulator-sanctioned mechanisms for sourcing a specific unapproved medicine for a specific patient, typically requiring documentation of unmet medical need and local regulatory or ethics-committee sign-off.^[28]

These pathways exist precisely because a molecule can show meaningful, peer-reviewed clinical benefit — as sac-TMT has across several oncology indications — well before it completes full regulatory review in every market where patients might need it. Understanding that such mechanisms exist, and how they are structured, is a relevant piece of context for any physician or patient navigating a diagnosis where the most current data on a therapy originates from a jurisdiction where that therapy is not yet locally licensed.

What This Means for Physicians and Patients

For oncologists and treating physicians, sac-TMT represents an actively evolving option within the TROP2-ADC class, with the most mature efficacy and regulatory data currently concentrated in China across TNBC, HR+/HER2- breast cancer, and EGFR-mutated NSCLC. Physicians outside jurisdictions where the drug is approved should be aware that sac-TMT is investigational in their region and not part of standard-of-care guidelines outside its approved indications, and should rely on locally approved prescribing information, regulatory guidance, and clinical trial enrolment pathways where relevant.

For patients, it is important to understand that sac-TMT's availability depends entirely on regulatory approval status in a given country. A Breakthrough Therapy Designation or ongoing Phase 3 trial does not mean a drug is approved or accessible for routine treatment. Patients interested in clinical trial participation should discuss eligibility with their treating oncologist or refer to public trial registries such as ClinicalTrials.gov.

References

1. Sofianidi AA, et al. Sacituzumab tirumotecan (sac-TMT/MK-2870/SKB264): a novel antibody–drug conjugate in breast cancer. Oncology Reviews. 2026. DOI: 10.3389/or.2026.1781533
2. Frontiers in Oncology. Sacituzumab tirumotecan (sac-TMT/MK-2870/SKB264): a novel antibody–drug conjugate in breast cancer (full text). frontiersin.org
3. Annals of Oncology. Sacituzumab tirumotecan in participants with advanced or metastatic urothelial carcinoma and disease progression after chemotherapy and immune checkpoint inhibitors. 2025.
4. ClinicalTrials.gov. NCT06841354, NCT06356311, and related sac-TMT/MK-2870 registrational study records, Merck Sharp & Dohme LLC.
5. Xu B, et al. Sacituzumab tirumotecan in previously treated metastatic triple-negative breast cancer: a randomized phase 3 trial (OptiTROP-Breast01). Nature Medicine. 2025.
6. Targeted Oncology. Sac-TMT Improves PFS in HR+/HER2− Metastatic Breast Cancer (OptiTROP-Breast02 coverage). 2026.
7. Kelun-Biotech. Announces Fourth Indication for Sacituzumab Tirumotecan (sac-TMT) Approved by NMPA in HR+/HER2- Breast Cancer. PRNewswire, February 6, 2026.
8. ASCO 2025 coverage. OptiTROP-Lung03 Evaluates Sacituzumab Tirumotecan in EGFR-Mutated NSCLC.
9. Velez MA, et al. Sacituzumab tirumotecan and the expanding role of TROP2-directed therapy in EGFR-mutant NSCLC. Shanghai Chest. 2026.
10. Sacituzumab Tirumotecan in EGFR-TKI–Resistant, EGFR-Mutated Advanced NSCLC (OptiTROP-Lung04). New England Journal of Medicine. 2026. DOI: 10.1056/NEJMoa2512071
11. OncLive. Sacituzumab Tirumotecan NDA for Pretreated EGFR+ NSCLC Accepted for Review in China.
12. Sacituzumab tirumotecan plus pembrolizumab versus pembrolizumab in PD-L1-positive advanced NSCLC (OptiTROP-Lung05): interim analysis. The Lancet. 2026. DOI: 10.1016/S0140-6736(26)00968-2
13. OncLive. OptiTROP-Lung05 Shows PFS Benefit With First-Line Sac-TMT Plus Pembrolizumab in PD-L1+ NSCLC.
14. Annals of Oncology. Sac-TMT in advanced/metastatic urothelial carcinoma, cohort 9 of study 2870-001/KL264-01.
15. ClinicalTrials.gov. NCT07088211 — Sacituzumab Tirumotecan and Toripalimab in First-line Treatment of HNSCC.
16. Fred Hutchinson Cancer Center. A Clinical Study of Sacituzumab Tirumotecan (Sac-TMT, MK-2870) in People With Breast Cancer (MK-2870-032).
17. CancerNetwork. Sacituzumab Tirumotecan Granted Breakthrough Therapy Designation for NSCLC — safety data summary.
18. Synapse (PatSnap). Sacituzumab Tirumotecan clinical update — OptiTROP-Breast05 dosing and safety data.
19. OncLive. Sacituzumab Tirumotecan Earns Approval in China in Pretreated Advanced TNBC.
20. OncLive. China's NMPA Approves Sacituzumab Tirumotecan for Pretreated EGFR+ Advanced NSCLC.
21. Kelun-Biotech / PRNewswire. Third Indication for Kelun-Biotech's TROP2 ADC Sac-TMT Approved for Marketing by NMPA in EGFRm NSCLC Following Progression on EGFR-TKI Therapy. October 11, 2025.
22. pharmaphorum. Kelun gets world-first approval for TROP2 ADC.
23. Merck & Co. FDA Grants Breakthrough Therapy Designation to Sacituzumab Tirumotecan (sac-TMT) for the Treatment of Certain Patients With Previously Treated Advanced or Metastatic Nonsquamous NSCLC With EGFR Mutations. Press release, December 3, 2024.
24. OncLive. Sac-TMT Plus Pembrolizumab Nets Breakthrough Therapy Designation in China for First-Line PD-L1+ NSCLC (includes FDA BTD timeline context).
25. U.S. Food and Drug Administration. Expanded Access. fda.gov/news-events/public-health-focus/expanded-access
26. Scepura M, et al. Oncology Expanded Access and FDA's Project Facilitate. The Oncologist. 2021. DOI: 10.1002/onco.13910
27. Whicher DM, et al. Early Access Provision for Innovative Medicinal Products in Oncology: Challenges and Opportunities. Frontiers in Medicine (PMC7492559).
28. myTomorrows. Understanding Expanded Access, Compassionate Use and Similar Terms.

Compiled from peer-reviewed journals (Nature Medicine, New England Journal of Medicine, The Lancet, Oncology Reviews, Shanghai Chest), ClinicalTrials.gov registry records, and public regulatory/company announcements available as of July 2026. Clinical research in this area is ongoing and findings may be updated by subsequent publications or regulatory actions.