Serum levels of vascular endothelial growth factor (VEGF) in systemic sclerosis (SSc) patients with and without fingertip ulcers. Compared with healthy controls, serum levels of VEGF were increased in patients with fingertip ulcers. In patients without fingertip ulcers, however, levels of VEGF were even more enhanced, indicating that VEGF might be protective against the development of fingertip ulcers if its serum concentration exceeds a certain threshold level. Data are shown as box plots, with upper and lower quartiles shaded. #P < 0.05.