NCI has collaborated with the Cancer Institute of the Chinese Academy of Medical Sciences (CICAMS) on a series of studies to develop early detection and treatment methods for esophageal squamous cell carcinoma (ESCC) and its precursor lesion, squamous dysplasia. This research has four parts: (1) primary screening studies, to develop accurate, cost-effective and patient-acceptable primary screening tests for esophageal precursor and early invasive lesions; (2) endoscopic localization studies, to endoscopically visualize foci of dysplasia and early cancer; (3) endoscopic therapy studies, to develop focal curative endoscopic therapies for high-grade dysplasias and early invasive cancers; and (4) chemoprevention studies, to evaluate the ability of oral chemopreventive agents to reduce progression or cause regression of low-grade esophageal dysplasias. Recently, a randomized, placebo-controlled clinical trial was conducted to evaluate the potential chemopreventive effects of selenomethionine (an inorganic selenium) and celecoxib (a COX-2 selective non-steroidal anti-inflammatory drug) on patients with mild or moderate squamous dysplasia. Among the patients who began the trial with mild dysplasia, those who took selenomethionine had significantly more regression and less progression of their dysplasia than those who did not take this agent. This result is the first positive finding for any candidate ESCC chemopreventive agent in a randomized controlled trial.