A first-in-human clinical trial of an experimental antibody-drug conjugate targeting the protein B7-H4 has reported partial tumor responses in patients with advanced or metastatic ovarian, endometrial and breast cancer, according to results from the Phase 1/2a BLUESTAR study published in Nature Communications. The drug, AZD8205, known as puxitatug samrotecan, was tested in 47 patients with B7-H4-positive solid tumors who had received prior treatment, marking the first time this agent has been evaluated in humans.
B7-H4 is a protein found at high levels in several solid tumors while showing limited expression in normal tissue, making it an attractive target for targeted cancer therapy. The molecule also plays a biological role in tumor progression: it negatively regulates T-cell function, and high B7-H4 expression has been associated with disease advancement. These properties positioned B7-H4 as a promising anchor for an antibody-drug conjugate, a class of therapy that pairs an antibody directed against a tumor-specific marker with a potent cell-killing payload.
AZD8205 combines a B7-H4-directed antibody with a topoisomerase-1 inhibitor, a type of chemotherapy payload, connected through a stable cleavable linker. This design allows the drug to release its toxic payload inside B7-H4-expressing tumor cells and also exert a bystander effect on neighboring tumor cells that may not express the target themselves. Patients in the trial received the drug intravenously at doses ranging from 0.8 to 3.2 milligrams per kilogram every three weeks.
The study’s primary objectives were to evaluate the safety and tolerability of puxitatug samrotecan, including the incidence of adverse events, serious adverse events and dose-limiting toxicities, and to determine the maximum tolerated dose and/or recommended phase 2 dose. Secondary objectives included characterizing the drug’s pharmacokinetics, assessing antitumor activity measured by objective response rate, and determining its pharmacodynamics. The trial is registered as ClinicalTrials.gov NCT05123482.
Safety findings showed that the most common treatment-related adverse events were nausea, affecting 51.1 percent of patients, neutropenia, affecting 48.9 percent, and anemia, affecting 38.3 percent. At the highest dose tested, 3.2 milligrams per kilogram, dose-limiting neutropenia and thrombocytopenia were observed, indicating that blood-cell toxicities defined the upper boundary of tolerability for this agent.
Among patients treated at doses of 1.6 milligrams per kilogram or higher, a range identified as the predicted efficacious exposure, partial responses were documented in ovarian, endometrial and breast cancer. Across this group, the objective response rate was 20.5 percent, with 9 of 44 patients achieving a partial response. The investigators characterized the overall safety profile as manageable and the efficacy signals as promising in this heavily pretreated population.
Translational analyses accompanying the trial provided mechanistic support for the drug’s design. These data indicated selective localization of the topoisomerase-1 inhibitor payload to B7-H4-expressing tumor cells, consistent with the antibody delivering its cargo preferentially to cells carrying the target protein. The analyses also showed induction of target-dependent DNA damage, the expected downstream consequence of topoisomerase-1 inhibition within tumor cells.
The findings establish initial clinical proof of concept for B7-H4 as an antibody-drug conjugate target in solid tumors. Because the trial enrolled patients whose cancers had progressed despite earlier therapy, the response signals carry particular weight for treatment options in ovarian, endometrial and breast cancer, tumor types where B7-H4 expression is frequently observed. Further development of puxitatug samrotecan is ongoing, with subsequent studies expected to refine dosing and expand testing across B7-H4-positive malignancies.
As with all first-in-human studies, the trial was designed primarily to establish safety and identify a tolerable dose rather than to demonstrate definitive efficacy. The patient numbers were small, the responses were partial rather than complete, and the results will require confirmation in larger, controlled studies. Nevertheless, the combination of a manageable toxicity profile, objective responses at biologically active doses and mechanistic evidence of selective payload delivery positions this B7-H4-directed agent among a growing class of antibody-drug conjugates now advancing through early-phase clinical testing in hard-to-treat solid tumors.
Subject of Research: A first-in-human Phase 1/2a trial of the B7-H4-directed antibody-drug conjugate AZD8205 in advanced solid tumors
Article Title: B7-H4‒directed antibody-drug conjugate AZD8205 (puxitatug samrotecan) in patients with advanced/metastatic solid tumors: the Phase 1/2a (BLUESTAR), first-in-human study
Article References: Meric-Bernstam, F., Naito, Y., Gaillard, S., Shimoi, T., Chung, V., Davis, A. A., Proia, T. A., Wang, J., Dubois, V. F. S., Rebelatto, M. C., McFarlane, M., Kulkarni, M., Upadhyay, S., Tian, J., Miller, N., Luheshi, N., Varga, A., Oh, D.-Y., & Mileshkin, L. (2026). B7-H4‒directed antibody-drug conjugate AZD8205 (puxitatug samrotecan) in patients with advanced/metastatic solid tumors: the Phase 1/2a (BLUESTAR), first-in-human study. Nature Communications. https://doi.org/10.1038/s41467-026-78925-8
Image Credits: AI Generated
DOI: 10.1038/s41467-026-78925-8
Keywords: B7-H4, antibody-drug conjugate, AZD8205, puxitatug samrotecan, BLUESTAR trial, ovarian cancer, endometrial cancer, breast cancer, topoisomerase-1 inhibitor, first-in-human study, dose-limiting toxicity, objective response rate
News Source: Nathaniel Bowman. (October 30, 2026). First-in-human trial shows B7-H4 antibody-drug conjugate shrinks ovarian, endometrial and breast tumors. Scienmag.
