The vast majority of people who have Barrett's oesophagus don't develop oesophageal cancer. If the abnormal cells in the oesophagus do become cancerous, first they go through a series of pre-cancerous changes called dysplasia. Dysplasia is classified as low-grade or high-grade, depending on how abnormal the cells are. High-grade is the most abnormal and means that the cells are at most risk of becoming cancerous.
Attribution: BUPA