The phrase "shrank or eliminated" appeared in every bullet point of the presentation GSK delivered at the Society of Gynecologic Oncology's annual meeting in Puerto Rico [1]. It's doing a lot of work. "Shrank" and "eliminated" are not the same outcome, one means the tumour got smaller, the other means it's gone, but they're yoked together in the trial results for Mocertatug Rezetecan, the antibody-drug conjugate GSK acquired from China's Hansoh Pharma in late 2023 [1]. That yoking is the story.
Mo-Rez posted a 62% response rate in ovarian cancer patients where chemotherapy had already failed [1]. In endometrial cancer, the figure was 67% [1]. GSK is already planning five late-stage global trials in the next few months, including on patients in the UK [1]. The company expects Mo-Rez to reach peak annual sales of more than £2bn [1]. But the presentation hasn't broken out how many tumours were eliminated versus merely shrank, or by how much.
salvage population
The trial enrolled 224 patients around the world over the past year [1]. All of them had already failed chemotherapy. This is what oncologists call a salvage population, patients with few options left. That context makes 62% remarkable. It also frames what "response" actually measures: not survival, not cure, but whether the tumour changed size in a way that could be detected on imaging.
Mo-Rez is an antibody-drug conjugate, administered every three weeks via intravenous infusion [1]. The mechanism is a guided missile, not a carpet bomb. The antibody binds to a protein overexpressed on cancer cells; the drug payload kills the cell from inside. ADCs are having a moment. GSK's other gynecologic cancer drug, Jemperli, grew 89% last year [1]. Most of the hottest cancer drugs in development right now are ADCs.
The most common side-effect was nausea, and only a few patients needed to stop treatment [1]. That's the reassurance GSK is selling alongside efficacy: a drug that works in a population where chemo didn't, without the toxicity profile that makes chemo unbearable.
strategic reversal
GSK sold its entire cancer portfolio to Novartis in 2015 in exchange for the Swiss company's vaccines business [1]. The deal was framed as a strategic exit, GSK would focus on vaccines and respiratory drugs, leave oncology to others. Now it has four approved cancer medicines and 13 in clinical development [1]. Oncology sales last year were nearly £2bn, up 43% from 2024 [1].
Luke Miels became GSK's chief executive on 1 January [1]. The company has a 2031 sales target of £40bn [1]. AstraZeneca's turnover last year outstripped GSK's near-£33bn by more than £10bn, and AstraZeneca's market value is more than twice as high [1]. The reversal isn't just about Mo-Rez. It's about whether GSK can close the gap by shopping in Hangzhou instead of building in-house.
Endometrial cancer affects 1.6 million women globally, with 417,000 new cases each year [1]. Ovarian cancer affects 843,000 people, with 240,000 new cases annually [1]. The five trials GSK plans will test whether the 62% holds at scale, and whether "shrank or eliminated" translates to longer survival. For now, the phrase is doing two things at once: it's technically accurate, both outcomes count as a response, and it's a hedge. We don't know yet how many patients are actually cancer-free.
For 224 patients who had run out of chemotherapy options, 62% is a door opening. The next five trials will show whether it stays open.
The drug's approval in the US is expected later this year, with European regulators likely to follow in 2026 [1]. If Mo-Rez succeeds, it won't just be a win for GSK's oncology comeback, it will validate a model where Western pharma giants license Chinese innovation rather than compete with it.
