Overweight and obese individuals are two times more likely than healthy weight people to develop a type of esophageal cancer called esophageal adenocarcinoma. A smaller increase in risk has been found for gastric cardia cancer, a type of stomach cancer that begins in the area of the stomach next to the esophagus. Most studies have not observed increases in risk with obesity in another type of esophageal cancer, squamous cell cancer. An increased risk of esophageal adenocarcinoma has also been associated with weight gain, smoking, and being younger than age.
The mechanisms by which obesity increases risk of adenocarcinoma of the esophagus and gastric cardia are not well understood. One of the leading mechanisms proposed has been that increases in gastric reflux due to obesity may increase risk. However, in the few studies that have examined this issue, risk associated with body mass index (BMI) was similar for those with and without gastric reflux.
This answer is based on source information from the National Cancer Institute.