In lewis lung cancer cells, overexpression of IDO enhanced Janus tyrosine kinase 2 (JAK-2) and STAT3 phosphorylation and up-regulated the production of Matrix metalloproteinase-2 (MMP-2) and MMP-9, two essential genes involved in invasion and metastasis [28] (Fig. 1). Here, IDO1 is linked to lung carcinoma.