PAI-1 in Skin Malignancies: a Central Regulator of Tumor Progression and Therapeutic Resistance.

Opinion statement: Plasminogen activator inhibitor-1 (PAI-1) plays a multifaceted and central role in the tumor biology of various skin malignancies. Beyond its classical function in fibrinolysis, PAI-1 contributes to tumor progression by promoting immunosuppression, angiogenesis, cellular senescence, and tissue remodeling. Its expression is particularly elevated in aggressive disease stages across cutaneous melanoma, cutaneous squamous cell carcinoma (cSCC), cutaneous angiosarcoma (CAS), and mycosis fungoides (MF), and is associated with poor clinical outcomes. The ability of PAI-1 to induce senescence-associated secretory phenotype (SASP), modulate PD-L1 expression, and recruit tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs) suggests a key role in shaping the immunosuppressive tumor microenvironment (TME). This positions PAI-1 as both a potential biomarker for disease progression and a therapeutic target for restoring immune responsiveness, especially in tumors resistant to immune checkpoint inhibitors (ICIs). The PAI-1 inhibitor TM5614 has demonstrated promising activity in early clinical studies, particularly in anti-PD-1-refractory melanoma, and is currently under evaluation in multiple Phase II and III trials. Future strategies should focus on patient stratification using biomarkers such as SASP factors and PAI-1 levels, as well as rational combination therapies targeting interconnected pathways like IL-17/IL-23, AhR, and senescence signaling. Overall, PAI-1 inhibition offers a novel and mechanistically grounded approach to improve outcomes in skin cancers characterized by therapy resistance and an immunosuppressive microenvironment.