There are 4 main layers of the esophageal wall: mucosa, submucosa, muscularis propria, and adventitia. The mucosa is further divided into the epithelium, lamina propria, and muscularis mucosae. Dysplasia is confined to the epithelium. Intramucosal tumors (T1a) invade the lamina propria or muscularis mucosae. Tumors that invade the submucosa are classified T1b. T2 tumors invade the muscularis propria, T3 tumors invade the adventitia, and T4 tumors invade adjacent structures.