PTK2 and squamous cell carcinoma: Many other signaling pathways have been reported to be associated with uPAR, including the focal adhesion kinase (FAK), EGFR, and Ras–mitogen-activated protein kinase (MAPK) pathways (epidermoid carcinoma) [22, 39], as well as the ERK pathway through formyl peptide receptor-like 1 (FPRL1; THP-1, macrophage), which is a G-protein-coupled receptor [40].