Id1 promotes carcinogenesis and metastasis, and predicts prognosis of non-small cell lung cancer (NSCLC)-adenocarcionoma patients. We hypothesized that Id1 may play a critical role in lung cancer colonization of the liver by affecting both tumor cells and the microenvironment. Depleted levels of Id1 in LLC (Lewis lung carcinoma cells, LLC shId1) significantly reduced cell proliferation and migration in vitro. Genetic loss of Id1 in the host tissue (Id1(-/-) mice) impaired liver colonization and increased survival of Id1 animals. Histologically, the presence of Idl in tumor cells of liver metastasis was responsible for liver colonization. Microarray analysis comparing liver tumor nodules from Id1(+/+) mice and Idl(-/-) mice injected with LLC control cells revealed that Id1 loss reduces the levels of EMT-related proteins, such as vimentin. In tissue microarrays containing 532 NSCLC patients' samples, we found that Idl significantly correlated with vimentin and other EMT-related proteins. Idl loss decreased the levels of vimentin, integrin beta 1, TGF beta 1 and snail, both in vitro and in vivo. Therefore, Id1 enables both LLC and the host microenvironment for an effective liver colonization, and may represent a novel therapeutic target to avoid NSCLC liver metastasis. (C) 2017 Elsevier B.V. All rights reserved.