Discover how GSK’s newly licensed cancer drug, Mo-Rez, achieved a massive 67% response rate in 2026 clinical trials for ovarian and endometrial cancers.
In the high-stakes world of oncology, finding a therapy that aggressively targets tumors while sparing healthy tissue is the ultimate holy grail. What if the next major leap in treating platinum-resistant ovarian and endometrial cancer was already here—and it came from a massive cross-border licensing deal?
In April 2026, British pharmaceutical giant GSK revealed data from its Phase I BEHOLD-1 clinical trial, and the numbers are turning heads across the biotech industry. Mocertatug rezetecan (Mo-Rez), a novel cancer drug licensed from China’s Hansoh Pharma, demonstrated a staggering 67% objective response rate in advanced endometrial cancer and 62% in platinum-resistant ovarian cancer.
For patients who have exhausted traditional chemotherapy options, these figures aren’t just promising—they represent a potential paradigm shift.
Under the aggressive leadership of new CEO Luke Miels, GSK is betting heavily on the booming antibody-drug conjugate (ADC) market, which analysts project will reach $31 billion by 2030. In this guide, we’ll break down exactly what Mo-Rez is, analyze the 2026 trial data, explore why targeting the B7-H4 protein is a game-changer, and look at what this means for patients and investors alike.
What is Mocertatug Rezetecan (Mo-Rez)?
Mocertatug rezetecan (formerly HS-20093) is an investigational antibody-drug conjugate (ADC) designed specifically to target the B7-H4 antigen, a protein heavily expressed in certain solid tumors but rarely found in healthy tissue.
Think of an ADC as a biological “smart bomb.” It consists of three parts:
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The Monoclonal Antibody: A homing device trained to find and bind exclusively to the B7-H4 protein on the surface of cancer cells.
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The Payload: A highly potent topoisomerase inhibitor (a type of chemotherapy).
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The Linker: The chemical bridge holding them together, which only releases the toxic payload once the antibody has penetrated the cancer cell.
Mo-Rez has a drug-to-antibody ratio (DAR) of 6, meaning each antibody carries six molecules of the cancer-killing payload, striking an optimal balance between efficacy and tolerability.
The 2026 BEHOLD-1 Trial Data Decoded
The buzz surrounding Mo-Rez stems directly from the BEHOLD-1 Phase I global trial data presented at the Society of Gynecologic Oncology (SGO) Annual Meeting in April 2026.
When dealing with late-stage, treatment-resistant gynaecological cancers, historical response rates to standard care are frustratingly modest. Mo-Rez shattered those benchmarks.
At the highest doses evaluated (5.8 mg/kg for ovarian and 4.8 mg/kg for endometrial), the confirmed Objective Response Rate (cORR)—which measures patients whose tumors shrank by at least 30% or disappeared—was exceptional:
| Cancer Type | Patient Profile | Confirmed ORR | Prior Treatment Context |
| Endometrial Cancer (EC) | Recurrent or advanced | 67% | Heavily pre-treated |
| Ovarian Cancer (PROC) | Platinum-resistant | 62% | Failed standard chemotherapy |
Hesham Abdullah, GSK’s global head of cancer R&D, didn’t mince words: “Do we think it would be a blockbuster? Yes, absolutely.” By achieving a >60% response rate in patients with platinum-resistant ovarian cancer (PROC), Mo-Rez provides a desperately needed lifeline. Currently, patients with PROC face an incredibly difficult prognosis, making these trial results a monumental win for precision oncology.
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Why Targeting B7-H4 Works
Why is the medical community so fixated on B7-H4 right now?
B7-H4 is an immune checkpoint protein. In a healthy human body, it’s barely detectable. However, in ovarian, endometrial, and breast cancers, tumors hijack B7-H4 and overexpress it to hide from the body’s immune system.
By specifically designing an ADC to hunt for B7-H4, researchers have achieved two things:
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High Precision: The drug ignores healthy cells, acting directly on the malignant tissue.
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Broad Application: The BEHOLD-1 trial showed that Mo-Rez was effective across a range of B7-H4 expression levels, not just the absolute highest ones. This broadens the total addressable market of patients who can benefit from the therapy.
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Side Effects & Safety Profile
No oncology drug is without side effects, but for an ADC carrying a highly toxic payload, Mo-Rez’s safety profile is manageable, allowing patients to stay on the medication longer.
Key Safety Metrics from BEHOLD-1:
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Low Dropout Rate: At the highest doses, only 0% of ovarian cancer patients and 4% of endometrial cancer patients discontinued treatment due to treatment-related adverse events (TRAEs).
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Common Side Effects: The most frequent issue was nausea (82% in PROC; 75% in EC), along with fatigue and alopecia.
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Hematologic Issues: Grade ≥3 TRAEs (severe side effects) were mostly blood-related, such as neutropenia (decreased white blood cells) and anaemia. This is standard and expected for topoisomerase inhibitor ADCs.
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Lung Safety: Rates of interstitial lung disease or pneumonitis—a severe risk with some ADCs—were incredibly low (3%, or 5 out of 178 patients), and all cases were mild to moderate.
The GSK & Hansoh Pharma Deal: A $1.5 Billion Bet
The origin story of Mo-Rez is a masterclass in strategic licensing.
In late 2023, GSK paid $85 million upfront to China’s Hansoh Pharmaceutical Group for the exclusive commercialization rights to the drug everywhere except mainland China, Hong Kong, Macau, and Taiwan. The deal includes up to $1.5 billion in success-based milestone payments.
Why did GSK make this move? Over a decade ago, GSK practically exited oncology by swapping its cancer assets for Novartis’s vaccine business. But under former CEO Emma Walmsley, and now turbocharged by new CEO Luke Miels (who took the helm in January 2026), GSK is aggressively rebuilding its cancer portfolio.
With the global ADC market expected to hit $31 billion by 2030, grabbing a “pipeline in a product” like Mo-Rez gives GSK a direct shot at a multi-billion dollar blockbuster. It’s part of their larger mandate to hit a staggering £40 billion ($50+ billion) in total company sales by 2031.
Five Global Phase III Trials in 2026
With Phase I data this compelling, GSK isn’t waiting around. The company has announced an accelerated development timeline, bypassing traditional sluggish trial phases.
Starting in mid-to-late 2026, GSK will launch five pivotal global Phase III trials for Mo-Rez.
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BEHOLD-Ovarian01: Testing the drug at the recommended 5.8 mg/kg dose in platinum-resistant ovarian cancer.
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BEHOLD-Endometrial01: Testing the drug as a second-line treatment for endometrial cancer.
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Earlier Line Settings: The three other trials will assess if Mo-Rez can be used even earlier in a patient’s diagnosis, rather than waiting for them to fail chemotherapy first.
If these Phase III trials replicate the success of the BEHOLD-1 data, we could see regulatory submissions to the FDA and EMA shortly after, bringing this life-saving treatment to clinics worldwide.
What types of cancer does Mo-Rez treat?
Currently, Mo-Rez has shown exceptional results in treating recurrent or advanced endometrial cancer, as well as platinum-resistant ovarian cancer. Ongoing clinical trials will determine its efficacy in other solid tumors.
What were the results of the 2026 Mo-Rez clinical trials?
In the Phase I BEHOLD-1 trial reported in April 2026, Mo-Rez shrank tumors by at least 30% in 67% of endometrial cancer patients and 62% of platinum-resistant ovarian cancer patients, significantly outperforming historical standard-of-care expectations.
Who developed the cancer drug Mo-Rez?
The drug was originally developed by China's Hansoh Pharma. In 2023, GSK licensed the worldwide commercialization rights (excluding mainland China, Hong Kong, Macau, and Taiwan) for $85 million upfront and up to $1.5 billion in milestones.
What are the side effects of Mo-Rez?
The most common side effects observed in trials were nausea, fatigue, and temporary hair loss. Severe side effects were primarily hematologic, such as lowered white blood cell counts (neutropenia) and anemia, which are generally manageable in a clinical setting.
The 2026 readout for GSK’s mocertatug rezetecan is more than just a victory for a single pharmaceutical company; it’s a beacon of hope for hundreds of thousands of women battling hard-to-treat gynaecological cancers.
Key Takeaways:
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Unprecedented Efficacy: Achieving a 62-67% response rate in highly treatment-resistant ovarian and endometrial cancers proves the power of the B7-H4 targeted approach.
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Rapid Progression: GSK’s decision to immediately launch five global Phase III trials underscores the biotech industry’s confidence in this ADC framework.
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Market Dynamics: This highlights the growing trend of Western pharma giants licensing highly innovative, mature biotech assets from Chinese developers to supercharge their oncology pipelines.
As precision medicine evolves, antibody-drug conjugates like Mo-Rez represent the frontier of targeted, effective, and tolerable cancer care.
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