Over expression of human IDO1 in a constitutive manner has been demonstrated in the clinicopathologic study related to GC [83] and an experiment using GC cell lines demonstrated that IDO1 and COL12A1 can promote lymphatic metastasis of GC through positive feedback regulation of MAPK pathway mediated by kynurenine and integral protein β1 [84]. Here, COL12A1 is linked to gastric cancer.