FLT1 and rheumatic disorder: In recent years, accumulating evidence has suggested the pathological involvement of VEGF-A and its signaling pathways in the disease progression and associated pain in various rheumatic diseases, including RA, applying this growth factor as a hallmark of chronic pain and intensifying the study of VEGF-A and its cognate receptors, VEGFR-1 and VEGFR-2, as a therapeutic target for pain treatment [57,74].