Extracellular matrix, either produced by cancer cells or by cancer-associated fibroblasts, influences angiogenesis, invasion and metastasis. Chondroitin/dermatan sulfate (CS/DS) proteoglycans, which occur both in the matrix and at the cell surface, play important roles in these processes. The unique feature that distinguishes DS from CS is the presence of iduronic acid (IdoA) in DS. The main IdoA-producing enzyme, DS epimerase 1 (DS-epi1) was highly up-regulated in ESCC biopsies. To further understand the roles of IdoA in tumor development, DS-epi1 expression, and consequently IdoA content, was downregulated in ESCC cells. IdoA-deficient cells exhibited decreased migration and invasion capabilities in vitro, which was associated with reduced cellular binding of hepatocyte growth factor, inhibition of pERK-1/2 signaling, and de-regulated actin cytoskeleton dynamics and focal adhesion formation. Our findings demonstrate that IdoA in DS influences tumorigenesis by affecting cancer cell behavior. Overall design: Gene expression data including 10 Esophageal squamous carcinoma specimens and 27 gastroesophageal adenocarcinoma specimens.