VTCN1 (also called B7-H4) is an immune checkpoint molecule that negatively regulates T-cell activation and proliferation. It inhibits cytokine production and cytotoxic T-cell development, and when expressed on tumor-associated macrophages and dedifferentiated tumor cells, suppresses tumor-associated antigen-specific CD8+ T-cell immunity 1. VTCN1 expression is prevalent across multiple cancer types, including triple-negative breast cancer, ovarian cancer, hepatocellular carcinoma, and salivary gland adenoid cystic carcinoma 123. Recent evidence reveals that progesterone stimulates VTCN1 expression via the progesterone receptor-P300-BRD4 axis, linking female sex hormones to immune evasion in breast cancer 4. Multiple therapeutic strategies targeting VTCN1 are in development or clinical evaluation. These include antibody-drug conjugates such as XMT-1660 and B7-H4-ADC, which have demonstrated antitumor activity in breast and ovarian cancer models, including those resistant to platinum or PARP inhibitors 52. Additionally, abemaciclib, a CDK4/6 inhibitor, promotes VTCN1 degradation via lysosomal activation and enhances anti-tumor immunity, while NGI-1 inhibits B7-H4 glycosylation, improving immunogenicity when combined with chemotherapy and PD-L1 blockade in triple-negative breast cancer 67. Combinatorial blockade of VTCN1 and PD-1 synergistically enhances anti-tumor immune responses 8.