A first-in-human Phase 1/2a trial of the B7-H4-targeting antibody-drug conjugate puxitatug samrotecan reported partial responses across heavily pretreated ovarian, endometrial, and breast cancer patients. The program targets B7-H4, an immune- and tumor-associated antigen that can support ADC internalization into malignant cells. The report suggests early clinical activity for a class of patients who typically have limited options after multiple prior lines of therapy. As Phase 1/2a expands, safety characterization and dose selection will be key to determining whether efficacy can be sustained. For ADC competitors, early response signals can shape target validation and help inform biomarker strategies—particularly whether B7-H4 expression levels, tumor histology, or prior treatment exposure correlate with outcomes.