The present study revealed that the knockdown of Linc01559 markedly enhances the tumor malignant phenotypes of duodenal cancer cells, and the expression of Linc01559 is positively correlated with macrophage infiltration and acidic environment, suggesting that Linc01559 may act as a tumor promoter in the progression of duodenal adenocarcinoma and, thus, serve as a biomarker for clinical diagnosis. The gene discussed is LINC01559; the disease is neoplasm.