Definition

Stage I is divided into stages IA and IB, depending on where the cancer has spread. In stage IA, cancer has spread into the mucosa layer or thin muscle layer of the esophagus wall. The cancer cells are grade 1 or the grade is not known. Grade 1 cancer cells look more like normal cells under a microscope and grow and spread more slowly than grade 2 and 3 cancer cells. In stage IB, cancer has spread (1) into the mucosa layer, thin muscle layer, or submucosa layer of the esophagus wall. The cancer cells are any grade or the grade is not known; or (2) into the thick muscle layer of the esophagus wall. The cancer cells are grade 1.