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GSK (NYSE: GSK) reports Mo-Rez data in ovarian, endometrial cancer

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GSK plc reported encouraging early-stage results for mocertatug rezetecan (Mo-Rez), a B7-H4-targeted antibody-drug conjugate, in difficult-to-treat gynaecological cancers. In the phase 1 BEHOLD-1 trial, Mo-Rez monotherapy achieved confirmed objective response rates of 62% in platinum-resistant ovarian cancer and 67% in recurrent or advanced endometrial cancer at the highest doses tested.

The safety profile was described as manageable: very few patients stopped treatment because of treatment-related side effects, and serious side effects were mainly blood-related, which is typical for this drug class. Interstitial lung disease or pneumonitis occurred in 3% of patients and was mild to moderate. The median duration of response had not yet been reached at this interim analysis, suggesting responses may be durable but follow-up is ongoing.

On the back of these data, GSK plans to advance Mo-Rez into five pivotal global phase III trials in 2026 across ovarian and endometrial cancer settings, including earlier-line and maintenance use. This programme underscores GSK’s broader oncology strategy focused on antibody-drug conjugates and women’s cancers.

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Insights

Early Mo-Rez data look promising, but value depends on larger phase III trials.

The BEHOLD-1 phase 1 study shows high confirmed objective response rates of 62% in platinum-resistant ovarian cancer and 67% in recurrent or advanced endometrial cancer at the highest doses. These are difficult settings with historically modest response rates, so strong activity in a heavily pretreated population is noteworthy.

Safety appears manageable, with low treatment discontinuation due to adverse events and only 3% interstitial lung disease or pneumonitis, all mild to moderate. However, grade ≥3 treatment-related events were frequent and largely haematologic, so tolerability in broader populations remains an important consideration.

The plan to launch five pivotal phase III trials in 2026 signals strategic commitment and could meaningfully expand GSK’s oncology portfolio if results hold up. Actual impact will hinge on phase III outcomes, including durability of response, survival benefits and comparative safety versus existing therapies, which will emerge from future data readouts.

Confirmed objective response rate in PROC 62% Mo-Rez monotherapy at 5.8 mg/kg in platinum-resistant ovarian cancer
Confirmed objective response rate in EC 67% Mo-Rez monotherapy at 4.8 mg/kg in recurrent or advanced endometrial cancer
Patients with interstitial lung disease or pneumonitis 3% (5 of 178 patients) All cases grade 1–2 in BEHOLD-1
BEHOLD-1 total enrollment 224 patients 44 in phase 1a and 180 in phase 1b
Grade ≥3 treatment-related adverse events in PROC 64% At highest dose level in phase 1b
Grade ≥3 treatment-related adverse events in EC 54% At highest dose level in phase 1b
Planned pivotal phase III trials 5 trials Global Mo-Rez development starting in 2026
antibody-drug conjugate medical
"mocertatug rezetecan (or Mo-Rez for short), a novel antibody-drug conjugate (ADC) targeting the B7-H4 antigen"
An antibody-drug conjugate is a targeted medicine that combines an antibody, which can identify specific cells, with a powerful drug designed to destroy those cells. This approach allows for precise treatment, minimizing damage to healthy tissue. For investors, developments in this area can signal advances in cancer therapies and potential growth opportunities in the biotech sector.
objective response rate medical
"Mo-Rez monotherapy achieved confirmed objective response rates (cORR) of 62% ... and 67%"
The objective response rate (ORR) is the percentage of patients in a clinical trial whose tumors measurably shrink or disappear according to preset rules. Investors use it as a quick, objective signal of a drug’s ability to produce a clear treatment effect—like counting how many plants visibly respond after applying a new fertilizer—and higher ORR can improve odds of regulatory approval, commercial success, and company valuation.
platinum-resistant ovarian cancer medical
"confirmed objective response rates of 62% in platinum-resistant ovarian cancer (PROC)"
A form of ovarian cancer that stops responding to standard platinum-based chemotherapy, typically when the disease returns within about six months after treatment; think of it like a pest becoming resistant to a once-effective pesticide. It matters to investors because this resistance creates a large unmet medical need, shaping demand for new drugs, clinical trial strategies, regulatory priority and potential pricing — all of which can materially affect company value and market opportunity.
interstitial lung disease medical
"Overall rates of interstitial lung disease or pneumonitis were low (3%; 5 out of 178 patients)"
A group of lung conditions that cause inflammation and scarring of the thin tissue between the air sacs, which makes it harder for oxygen to pass into the blood; imagine the lungs’ fine filters becoming stiff and less effective. Investors care because reports of interstitial lung disease can affect a drug’s safety profile, trigger regulatory warnings or label changes, and shift demand for treatments or create liability risks that influence a company’s valuation.
phase III trials medical
"supports start of five pivotal phase III trials in 2026"
dose-limiting toxicity medical
"Primary endpoints included: incidence of dose-limiting toxicity in phase 1a"
Dose-limiting toxicity is a serious, treatment-related side effect observed in clinical trials that prevents researchers from safely increasing a drug’s dose. It matters to investors because these toxic effects set the maximum tolerated dose, influence whether a drug can reach levels that are effective, and therefore affect development timelines, costs, and the chance of regulatory approval — like a safety speed limit on how far a drug program can go.
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
Form 6-K
 
REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16
UNDER THE SECURITIES EXCHANGE ACT OF 1934
 
 
 
For the month of April 2026
 
Commission File Number 001-15170
 
 
GSK plc
(Translation of registrant's name into English)
 
 
79 New Oxford Street, London, WC1A 1DG
(Address of principal executive office)
 
 
 
Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.
 
Form 20-F . . . .X. . . . Form 40-F . . . . . . . .
 
 
 
 
Strictly embargoed until Sunday 12 April 2026, 3:10 pm (BST) / 10:10 (AST)
 
GSK presents positive data for B7-H4-targeted ADC in gynaecological cancers
 
●     Mocertatug rezetecan achieved confirmed objective response rates of 62% in platinum-resistant ovarian cancer (PROC) and 67% in recurrent or advanced endometrial cancer (EC) in BEHOLD-1 study
 
●     Current treatment options are limited for patients with PROC and EC
 
●     Promising efficacy and safety profile supports start of five pivotal phase III trials in 2026
 
 
 
GSK plc (LSE/NYSE: GSK) today announced positive findings from its global phase 1 BEHOLD-1 clinical trial for mocertatug rezetecan (or Mo-Rez for short), a novel antibody-drug conjugate (ADC) targeting the B7-H4 antigen. At the highest doses evaluated, Mo-Rez monotherapy achieved confirmed objective response rates (cORR) of 62% (5.8 mg/kg n=21/34; 95% CI: 44, 78) in platinum-resistant ovarian cancer (PROC) and 67% (4.8 mg/kg n=8/12; 95% CI: 35, 90) in recurrent or advanced endometrial cancer (EC).[1] These data will be presented for the first time in a late-breaking oral session at the Society of Gynecologic Oncology (SGO) Annual Meeting on Women's Cancer in San Juan, Puerto Rico.
 
Currently, there are limited treatment options with modest response rates for patients with PROC and advanced EC. B7-H4 is an immune checkpoint that is widely expressed in ovarian and endometrial cancers and is low in normal tissues, providing potential for a differentiated precision-therapy. The response to Mo-Rez observed across a range of B7-H4 expression levels reinforces its broad potential in gynaecologic cancers and further validates the relevance of targeting B7-H4.
 
Hesham Abdullah, Senior Vice President, Global Head Oncology, R&D, GSK, said: "Treatment of gynaecological cancers remains a major challenge, with a pressing need for new therapies that offer improved response rates. With Mo-Rez, we now have compelling evidence of a promising clinical profile, with response rates that support accelerating development into five pivotal global phase III trials later this year across ovarian and endometrial cancers, including earlier-line settings."
 
Ana Oaknin, Study Investigator for BEHOLD-1, Medical Oncology Department, Hospital Universitario Puerta de Hierro-Majadahonda, Madrid, Spain said: "In the early phase BEHOLD-1 study, we saw meaningful antitumour activity for this patient dataset, with response rates higher than typically seen in ADCs in development, and a manageable safety profile. For patients with platinum-resistant ovarian cancer and recurrent endometrial cancer, these findings are particularly encouraging."
 
At the highest doses evaluated in BEHOLD-1, few patients needed to stop treatment because of a treatment-related adverse events (TRAE) (0% in PROC and 4% in EC). The most common TRAE was nausea (82% in PROC; 75% in EC). Grade ≥3 TRAEs occurred in 64% and 54% patients in PROC and EC, respectively, and were predominantly haematologic, as expected for treatments in this class. Overall rates of interstitial lung disease or pneumonitis were low (3%; 5 out of 178 patients) and all cases were mild to moderate (grade 1-2). The interim analysis showed the median duration of response had not yet been reached. Based on the findings from this study, the recommended dose for the first of the phase III trials, BEHOLD-Ovarian01 and BEHOLD-Endometrial01, is 5.8 mg/kg.
 
About the BEHOLD clinical trial programme
The BEHOLD clinical programme is GSK's global development plan that includes the BEHOLD-1 (NCT06431594) monotherapy study and the ongoing BEHOLD-2 (NCT06796907) combination study. Mo-Rez will advance to five pivotal global phase III trials in 2026, starting with PROC (BEHOLD-Ovarian01 / NCT07286266) and 2L EC (BEHOLD-Endometrial01 / NCT07286331). Additional phase III studies will evaluate Mo-Rez in platinum-sensitive ovarian cancer (BEHOLD-Ovarian02) and in first-line maintenance settings for ovarian cancer without homologous recombination deficiency (BEHOLD-Ovarian03) and mismatch-repair-proficient endometrial cancer (BEHOLD-Endometrial02).
 
About BEHOLD-1
The BEHOLD-1 clinical trial is a two-part, open-label, phase 1 study evaluating the safety, tolerability and efficacy of Mo-Rez injection in patients with PROC or advanced/recurrent EC. Phase 1a assessed up to four Mo-Rez dose levels in patients with advanced solid tumours, with intravenous administration every three weeks until progression or toxicity. In the phase 1b dose expansion, patients with PROC or EC (1-3 prior lines of therapy) were randomised to three or two Mo-Rez dose levels, respectively.
 
At data cut-off, a total of 224 patients were enrolled in BEHOLD-1; n=44 in phase 1a (n=21 PROC, n=23 mix of other solid tumours) and n=180 in phase Ib (n=131 PROC, n=49 EC). Primary endpoints included: incidence of dose-limiting toxicity in phase 1a and confirmed ORR (cORR) by investigator per RECIST 1.1 in phase Ib. At the highest dose evaluated in phase Ib, the most common adverse events in PROC were nausea (86%), neutropenia/neutrophil count decreased (73%), anaemia (52%), fatigue (52%) and alopecia (52%). In EC, the most common adverse events were nausea (79%), neutropenia/neutrophil count decreased (58%), anaemia (54%), vomiting (46%) and fatigue (42%). Treatment-related adverse events led to dose interruptions in 39% of patients with PROC and 21% of those with EC, and to dose reductions in 39% in PROC and 17% in EC, at the highest dose. The trial is ongoing and currently in the dose expansion phase.
 
About mocertatug rezetecan
Mo-Rez is a novel investigational B7-H4-targeted antibody-drug conjugate designed to optimise efficacy and tolerability. It is composed of a fully human anti-B7-H4 monoclonal antibody covalently linked to a topoisomerase inhibitor payload and has a drug-to-antibody ratio (DAR) of 6. GSK acquired exclusive worldwide rights (excluding China's mainland, Hong Kong, Macau, and Taiwan) from Hansoh Pharma to progress clinical development and commercialisation of Mo-Rez globally.
 
About ovarian cancer and endometrial cancer
Endometrial cancer affects 1.6 million people globally, with 417,000 new cases each year and 15% to 20% of patients presenting in later stages of the disease.[2],[3] Ovarian cancer affects 843,000 people with 240,000 new cases annually.[4] 70% of these patients present with advanced disease.[5] Recurrence is common in advanced cases of disease, up to 67% in endometrial cancer and 70% in ovarian cancer, and survival usually declines after recurrence.[6],[7]
 
GSK in oncology
Our ambition in oncology is to help increase overall quality of life, maximise survival and change the course of disease, expanding from our current focus on blood and women's cancers into lung and gastrointestinal cancers, as well as other solid tumours. This includes accelerating priority programmes such as antibody-drug conjugates targeting B7-H3 and B7-H4, and IDRX-42, a highly selective KIT tyrosine kinase inhibitor.
 
About GSK
GSK is a global biopharma company with a purpose to unite science, technology, and talent to get ahead of disease together. Find out more at www.gsk.com.
 
 
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Cautionary statement regarding forward-looking statements
GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Such factors include, but are not limited to, those described in the "Risk Factors" section in GSK's Annual Report on Form 20-F for 2025.
 

Registered in England & Wales:
No. 3888792
 
 
Registered Office:
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References
 
 
[1] Oaknin A, McKean W, van Dongen M et al. Mocertatug Rezetecan (GSK5733584), a B7-H4 Targeted Antibody Drug Conjugate, in Platinum-Resistant Ovarian Cancer and Endometrial Cancer: First Results from the Global BEHOLD-1 Study. Presented at the Society of Gynecologic Oncology (SGO) Annual Meeting on Women's Cancer 2026. April 2026.
[2] Sung H, Ferlay J, Siegel R, et al. Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries. CA Cancer J Clin. 2021;71(3):209-249. doi:10.3322/caac.21660.
[3] CMP: CancerMPact® Patient Metrics Mar-2023, Cerner Enviza.
[4] Ren Y, Xu R, Wang Y, Su L, Su J. Global, regional, and national burden of ovarian cancer in women aged 45 + from 1990 to 2021 and projections for 2050: a systematic analysis based on the 2021 global burden of disease study. J Cancer Res Clin Oncol. 151(8):225. doi:10.1007/s00432-025-06277-9.
[5] Rauh-Hain JA, Krivak TC, Del Carmen MG et al. Ovarian cancer screening and early detection in the general population. Rev Obstet Gynecol. 2011;4(1):15-21.
[6] Shelvin KB, Vincent J, Morron S, Morin M, Mammoser A, Nair N. Recurrent high grade serous endometrial cancer with brain metastases: Immunotherapy confers improved quality of life and survival. Gynecol Oncol Rep. 2024;55:101494. doi:10.1016/j.gore.2024.101494.
[7] Salas Bolívar P, Gonzalez-Benitez C, Carbonell López M, Díez Sebastian J, Hernández Gutiérrez A, Zapardiel I. Prognostic Factors After the First Recurrence of Ovarian Cancer. Journal of Clinical Medicine. 2025; 14(2):470. https://doi.org/10.3390/jcm14020470.
 

 
SIGNATURES
 
 
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorised.
 
GSK plc
 
(Registrant)
 
 
Date: April 13, 2026
 
 
 
 
By:/s/ VICTORIA WHYTE
--------------------------
 
 
 
Victoria Whyte
 
Authorised Signatory for and on
 
behalf of GSK plc


FAQ

What did GSK (GSK) report about Mo-Rez in ovarian cancer?

GSK reported that Mo-Rez achieved a confirmed objective response rate of 62% in platinum-resistant ovarian cancer at the highest phase 1 dose, indicating substantial tumour shrinkage in many patients who typically have few effective treatment options.

How effective was GSK’s Mo-Rez in endometrial cancer according to the 6-K?

In recurrent or advanced endometrial cancer, Mo-Rez reached a confirmed objective response rate of 67% at the highest dose tested, suggesting strong anti-tumour activity in a setting where current treatments often produce only modest response rates.

What safety profile for Mo-Rez did GSK (GSK) describe in BEHOLD-1?

GSK described a manageable safety profile, with few treatment discontinuations due to side effects and serious events mainly blood-related. Interstitial lung disease or pneumonitis occurred in 3% of patients and was mild to moderate, aligning with expectations for this drug class.

What future trials of Mo-Rez did GSK (GSK) announce?

GSK plans five pivotal global phase III trials in 2026, including BEHOLD-Ovarian01 and BEHOLD-Endometrial01, plus additional studies in platinum-sensitive ovarian cancer and first-line maintenance settings for ovarian and endometrial cancers, expanding Mo-Rez across multiple disease stages.

What is Mo-Rez and how does it work in GSK’s oncology pipeline?

Mo-Rez is an investigational antibody-drug conjugate targeting the B7-H4 antigen, widely expressed in ovarian and endometrial cancers. It links a monoclonal antibody to a topoisomerase inhibitor payload, aiming to deliver chemotherapy directly to tumour cells while limiting exposure in normal tissues.

Why is B7-H4 a relevant target in GSK (GSK) gynaecologic cancer research?

B7-H4 is an immune checkpoint highly expressed in ovarian and endometrial cancers but low in normal tissues, making it an attractive precision target. Responses to Mo-Rez across different B7-H4 expression levels support its potential relevance for a broad group of gynaecologic cancer patients.