Gastroesophageal junction adenocarcinoma: This is a serious form of cancer that originates in the area where the esophagus transitions into the stomach. Gastroesophageal junction adenocarcinoma is frequently lethal. Surgical operation and chemotherapy (adjuvant treatment) are used as treatments. People with Barrett's esophagus are at an increased risk for developing gastroesophageal junction adenocarcinoma. In Barrett's esophagus, the normal cells of the area of the esophagus that enters the stomach are replaced by a different type of cell. The new cell lining is not cancerous but can predispose to cancer development. Gastroesophageal junction adenocarcinoma is also referred to as esophagogastric junction adenocarcinoma.