GSK Advances B7-H4 ADC Mocertatug Rezetecan to Five Phase 3 Trials After Strong Phase 1b Data in Gynecological Cancers

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GSK's Phase 1b BEHOLD-1 trial of mocertatug rezetecan (Mo-Rez), a B7-H4-targeted ADC, showed confirmed objective response rates (ORR) of 62% in 34 platinum-resistant ovarian cancer (PROC) patients at 5.8 mg/kg and 67% in 12 endometrial cancer (EC) patients at 4.8 mg/kg12.

Responses remain durable with median follow-up of 6 months for PROC and 4 months for EC; low interstitial lung disease rate of ~3-4% (all grade 1-2)12.

Strong data prompts GSK to initiate five pivotal Phase 3 trials in 2026:
BEHOLD-Ovarian01 (PROC), Ovarian02 (platinum-sensitive), Ovarian03 (front-line HR-proficient ovarian), Endometrial01 (2L EC), and Endometrial02 (1L MMR-proficient EC)12.

Data presented at Society of Gynecologic Oncology (SGO) Annual Meeting in San Juan, Puerto Rico; GSK views Mo-Rez as a potential blockbuster asset13.

Mo-Rez licensed from Hansoh Pharma; GSK has existing sales in these cancers from Jemperli and Zejula totaling ~$1.8B last year1.

Sources:

1. https://www.fiercebiotech.com/biotech/gsk-ceos-scientific-courage-propels-plans-medley-phase-3-trials-adc

2. https://us.gsk.com/en-us/media/press-releases/gsk-presents-positive-data-for-b7-h4-targeted-adc-in-gynecological-cancers/

3. https://pharmaphorum.com/news/data-backs-gsks-ovarian-cancer-blockbuster-hopes