A Phase 1 Study of PF-07260437, a B7-H4 × CD3 Bispecific T-cell Engager, in Patients with Advanced or Metastatic Breast, Ovarian, and Endometrial Cancer

B7-H4 is overexpressed in various cancers, making it a promising target for cancer immunotherapy. This phase 1, open-label, first-in-human study in patients with advanced/metastatic breast, ovarian and endometrial cancer evaluates the safety, pharmacokinetics (PK), and anti-tumour activity of PF-07260437, a novel B7-H4xCD3 bispecific T-cell engager. Enrolled patients received escalating doses of PF-07260437 (with/without priming dose) subcutaneously every two weeks, with a starting dose of 100 µg. Primary objectives included determination of maximum tolerated dose (MTD)/recommended dose for expansion (RDE), safety and tolerability. Secondary objectives included PK parameters and immunogenicity. Bayesian logistic regression model (BLRM) was used to guide dose escalation. Thirty patients with advanced/metastatic breast, ovarian and endometrial cancer received the study treatment during dose escalation; all were female (median age, 61.0 [41–75] years). Four patients (13.3