Decoding tumors from fibroblast activation protein: A review of the latest diagnostic and therapeutic prospects

Fibroblast activation protein (FAP), as a molecule closely associated with the tumor microenvironment (TME), has garnered widespread attention in recent years. FAP is a type II transmembrane serine protease primarily expressed in cancer-associated fibroblasts (CAFs), and it plays a significant role in tumor growth, invasion, metastasis, and immune evasion processes. FAP is highly expressed in over 90 % of epithelial cancers, which makes it a satisfactory diagnostic marker on account of its exceptional sensitivity and specificity. Using radio or fluorescence-labeled FAP-specific molecular probes can materialize high-contrast tumor imaging, and thereby facilitate early detection and monitoring. With regard to treatment, FAP-targeting strategies like FAP enzyme activity inhibitors, FAP-specific Chimeric Antigen Receptor T-Cell (CAR-T) cells, and FAP vaccines have demonstrated tremendous potential to hinder tumor growth, lower tumor angiogenesis, and reinforce anti-tumor immunity. For strengthening efficacy and lessening damage to normal cells, these strategies can also be integrated with chemotherapy, radiotherapy, and immunotherapy. This article not only reviews the research progress of FAP in tumor diagnosis and treatment, but also explores its paramount role and potential in the tumor microenvironment.