The global Phase I BEHOLD-1 clinical trial for mocertatug rezetecan (Mo-Rez) has shown confirmed objective response rates (cORR) of 62% in platinum-resistant ovarian cancer (PROC) and 67% in recurrent or advanced endometrial cancer (EC). 

Mocertatug rezetecan is a novel antibody-drug conjugate (ADC) targeting the B7-H4 antigen. B7-H4 is an immune checkpoint that is widely expressed in ovarian and endometrial cancers and is low in normal tissues. 

GSK shared the new findings in a late-breaking oral session at the Society of Gynecologic Oncology (SGO) Annual Meeting on Women’s Cancer in San Juan, Puerto Rico. 

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.” 

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. 

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.”