Akeso, Inc. (HKEX: 9926) has dosed the first patient in a Phase II study evaluating its investigational TROP2/Nectin-4 bispecific antibody-drug conjugate AK146D1 with the PD-1/VEGF bispecific antibody ivonescimab in advanced breast cancer. The AK146D1-202 study is intended to explore the combination across HER2-negative disease, with Akeso highlighting first-line hormone receptor-positive, HER2-negative breast cancer and triple-negative breast cancer as important areas of interest.
The development moves AK146D1 deeper into clinical testing only about a year after Akeso reported the first patient enrolled in its first-in-human programme in July 2025. That speed is strategically significant, but first-patient dosing does not establish efficacy, safety superiority or a viable regulatory path. AK146D1 remains an investigational ADC, and the new Phase II trial will need to show whether the theoretical advantages of targeting two tumour-associated antigens translate into a clinically useful balance of response, durability and tolerability.
The timing also raises the competitive bar. Breast cancer has become one of the most active markets for antibody-drug conjugates, while TROP2-directed therapies have already gained regulatory traction across hormone receptor-positive, HER2-negative disease and triple-negative breast cancer. Akeso is therefore entering Phase II development in a field where being another active ADC is unlikely to be enough. The eventual differentiation case will depend on whether the TROP2/Nectin-4 architecture provides clinically meaningful advantages over established single-target ADC strategies and whether adding ivonescimab strengthens that proposition without creating an unacceptable toxicity burden.
What does the AK146D1-202 Phase II trial actually test in advanced breast cancer?
ClinicalTrials.gov lists AK146D1-202 as NCT07591090, a Phase II study evaluating the safety, tolerability, pharmacokinetics, immunogenicity and antitumour activity of AK146D1 with AK112, Akeso’s development code for ivonescimab. The study is recruiting and has an estimated enrolment of 200 patients. Its recorded start date is July 17, 2026, with primary completion currently estimated for September 2027.
Objective response rate assessed by investigators under RECIST 1.1 and treatment-emergent adverse events are among the primary outcomes. Secondary measures include progression-free survival, disease control rate, duration of response, time to response, overall survival, pharmacokinetics and anti-drug antibodies. That endpoint structure makes sense for a mid-stage oncology programme because Akeso first needs to understand whether sufficient activity exists to justify larger, more comparative development rather than demonstrate a definitive survival advantage at this stage.
The registered study is open label, and available registry information describes a non-randomised design. Eligible patients have locally advanced, recurrent or metastatic HER2-negative breast cancer that cannot be treated with curative surgery, along with measurable disease and generally preserved performance status. The absence of a Phase III-style randomised comparator means response rates from AK146D1-202 will have to be interpreted as signal-generating evidence, particularly if Akeso subsequently compares the numbers with results from unrelated ADC trials.
This distinction matters because the commercial ambition extends beyond later-line salvage therapy. Akeso specifically says it wants to examine the potential of the regimen in first-line HR+/HER2- disease and TNBC. Moving an experimental ADC combination toward earlier treatment creates a higher efficacy and safety threshold because patients may already have effective alternatives, and tolerance for additive toxicity generally becomes increasingly important when developers seek to move therapies toward less heavily pretreated populations.
Why could combining TROP2 and Nectin-4 in one ADC differentiate AK146D1?
AK146D1 is designed around a bispecific antibody that recognises both TROP2 and Nectin-4. Akeso couples that antibody through a cleavable MC-AAA linker to DXd, a topoisomerase I inhibitor payload. The company’s premise is that recognising two antigens could increase tumour coverage in biologically heterogeneous cancers, potentially reducing dependence on consistently high expression of a single target. That remains a therapeutic hypothesis rather than a demonstrated clinical advantage.
TROP2 is already a clinically validated ADC target in breast cancer. The United States Food and Drug Administration approved datopotamab deruxtecan in January 2025 for certain adults with unresectable or metastatic HR-positive, HER2-negative breast cancer after prior endocrine-based therapy and chemotherapy. Sacituzumab govitecan also has established HR-positive, HER2-negative indications, while its breast cancer position expanded significantly in June 2026 when the FDA approved first-line uses in unresectable locally advanced or metastatic TNBC, including a combination with pembrolizumab for PD-L1-positive disease.
Nectin-4 provides a different source of biological validation. Enfortumab vedotin is a Nectin-4-directed ADC with established use in urothelial cancer, demonstrating that Nectin-4 can function as a clinically actionable ADC target. That success does not establish that dual TROP2/Nectin-4 targeting will improve outcomes in breast cancer, however. The question for AK146D1 is whether combining those targets within a single ADC can increase effective tumour engagement or address heterogeneous antigen expression without compromising exposure in normal tissues.
If the approach works, the value may be less about simply adding another target and more about widening the population in which sufficient ADC delivery can occur. If it does not, the additional molecular complexity may fail to produce a meaningful clinical difference from established TROP2 ADCs. Phase II response data, biomarker analyses and eventually comparative trials will be needed before those competing possibilities can be separated.
Can ivonescimab add enough value to justify another complex first-line combination?
The second part of Akeso’s strategy is equally important. Ivonescimab simultaneously targets PD-1 and VEGF, combining checkpoint inhibition and anti-angiogenic activity within one bispecific antibody. The drug already has an extensive development programme and regulatory approvals in China in lung cancer, but its breast cancer development remains an expanding clinical programme rather than an established standard of care.
Akeso has generated an early breast cancer rationale in TNBC. Company-reported Phase II data presented at the 2025 European Society for Medical Oncology Immuno-Oncology Congress covered 36 patients treated with first-line ivonescimab plus chemotherapy, with 35 patients included in the efficacy analysis. Akeso reported an 80% objective response rate, 100% disease control rate and median progression-free survival of 15.2 months after longer follow-up, while overall survival remained immature. Those data came from a small early study and should not be interpreted as a head-to-head demonstration of superiority over other first-line TNBC regimens.
The signal was nevertheless sufficient to support continued development. China’s Center for Drug Evaluation granted ivonescimab Breakthrough Therapy Designation for first-line TNBC, and Akeso is conducting the randomised, double-blind Phase III HARMONi-BC1 study of ivonescimab plus chemotherapy in unresectable locally advanced or metastatic first-line TNBC. Breakthrough Therapy Designation can facilitate development and regulatory interaction, but it is not marketing approval and does not establish efficacy.
AK146D1-202 therefore represents a second question layered onto an existing ivonescimab breast cancer programme. Instead of asking only whether ivonescimab can improve on conventional immunotherapy combinations, Akeso is examining whether it can serve as an immuno-oncology backbone for internally developed ADCs. Success could give the company a vertically integrated combination portfolio. Failure would show the difficulty of assuming that individually promising mechanisms will necessarily produce additive clinical value when placed together.
Why safety may be as important as response rate for Akeso’s IO2.0 plus ADC2.0 thesis
Combination oncology development repeatedly runs into the same constraint: biological activity is valuable only if exposure can be maintained. ADCs can carry payload-related toxicities, while immune checkpoint and VEGF-directed therapies bring their own safety considerations. Combining an experimental DXd-containing ADC with simultaneous PD-1 and VEGF blockade therefore makes tolerability a central part of the development thesis rather than a secondary detail.
Akeso describes early AK146D1 findings as showing potent antitumour activity with a favourable safety profile, but the disclosed evidence remains early stage and does not yet establish the safety profile of the AK146D1 and ivonescimab combination in a large breast cancer population. The Phase II study’s explicit inclusion of adverse events alongside objective response rate among its primary outcomes reflects that uncertainty.
This will become particularly important if Akeso attempts to develop the combination in first-line disease. Higher response rates would be encouraging, but clinicians and regulators will also need to understand Grade 3 or higher toxicity, serious adverse events, dose reductions, treatment interruptions, discontinuations and any toxicity patterns associated with the topoisomerase I payload or the immunotherapy component. Duration of treatment will matter as well, because a regimen that generates early responses but cannot be maintained may struggle to deliver durable benefit.
The safety question also affects Akeso’s broader ADC2.0 claim. The company has positioned AK146D1 and other internally developed ADCs as attempts to overcome limitations associated with conventional ADC therapeutic windows. Phase II is where that proposition begins to become testable in larger patient groups, but establishing a genuinely wider therapeutic window will require dose-exposure data and a sufficiently mature safety dataset rather than descriptive statements about early tolerability.
How does the changing breast cancer ADC market raise the bar for AK146D1?
The competitive environment has changed particularly quickly since AK146D1 first entered human testing. In addition to TROP2-directed ADCs, trastuzumab deruxtecan has pushed HER2-directed ADC treatment into HR-positive disease with HER2-low and HER2-ultralow expression. The FDA expanded its indication in January 2025 to include unresectable or metastatic HR-positive, HER2-low or HER2-ultralow breast cancer after progression on one or more endocrine therapies in the metastatic setting.
That evolution means the future addressable population for AK146D1 cannot be defined merely as “HER2-negative breast cancer.” Treatment histories increasingly include ADC exposure, molecular subtype, HER2 expression level, PD-L1 status and previous endocrine or targeted therapies. A Phase II response signal will consequently become more informative if Akeso can identify which biomarker-defined populations derive the greatest benefit and whether activity persists across different levels of TROP2 and Nectin-4 expression.
The most compelling outcome would be evidence that dual targeting solves a specific clinical problem rather than simply delivering another topoisomerase I payload through a new antibody construct. That could mean activity across heterogeneous antigen-expression patterns, efficacy in populations underserved by existing immunotherapy approaches, a favourable tolerability profile or sufficiently durable responses to justify movement into randomised testing. None of those advantages has yet been demonstrated.
What milestones could move AK146D1 plus ivonescimab beyond an early Phase II signal?
The first meaningful milestone will be an interpretable Phase II dataset showing both response activity and tolerability. Objective response rate will provide an early measure of antitumour activity, but duration of response and progression-free survival will become increasingly important as follow-up matures. Biomarker analyses involving TROP2, Nectin-4 and potentially immune characteristics could be especially valuable in determining whether the bispecific architecture is doing something that a conventional single-target ADC would not.
Akeso will also have to decide how the programme fits alongside its expanding breast cancer portfolio. HARMONi-BC1 is already testing ivonescimab with chemotherapy in first-line TNBC, while the company has initiated another breast cancer programme combining ivonescimab with its HER3-directed ADC AK138D1. The parallel development strategy gives Akeso several opportunities to establish ivonescimab as a combination backbone, but it will eventually require evidence-based prioritisation among multiple potentially competing internal regimens.
AK146D1-202 is therefore more consequential than a routine first-patient announcement, but not because dosing itself validates Akeso’s IO2.0 plus ADC2.0 strategy. Its importance comes from moving a highly differentiated molecular concept into a stage of development where clinical differentiation can begin to be measured. With TROP2 ADCs already established and breast cancer treatment moving rapidly toward increasingly sophisticated biomarker and combination strategies, AK146D1 will need to show more than activity. The eventual test is whether dual TROP2/Nectin-4 targeting combined with PD-1/VEGF inhibition can produce a response, durability and safety profile strong enough to justify randomised development against a standard of care that is itself continuing to improve.
