CD86 and neoplasm: In addition to the improvement of the tumor blood flow, the Wegiel and Otterbein’ group also reported that CO could induce apoptosis in lung cancers by altering the tumor microenvironment to increase the CD86 expression, and then activating mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases (Erk) 1/2 pathway [38].