The esophagus is a muscular tube that carries food and liquid from the mouth to the stomach. The esophagus is usually between 10 and 13 inches long. The normal adult esophagus is roughly three fourths of an inch across at its smallest point.
The wall of the esophagus has several layers. Cancer of the esophagus - also referred to as esophageal cancer - starts from its inner layer and grows outward. The layer that lines the inside of the esophagus is called the mucosa. The mucosa has 2 parts: the epithelium and the lamina propria. The epithelium forms the lining of the esophagus and is made up of flat, thin cells called squamous cells. The lamina propria is a thin layer of connective tissue right under the epithelium.
The next layer is the submucosa. Some parts of the esophagus have mucus-secreting glands in this layer. The layer under the submucosa is a thick band of muscle called the muscularis propria. This layer of muscle contracts in a coordinated, rhythmic way to force food along the esophagus from the throat to the stomach. The outermost layer of the esophagus is formed by connective tissue. It is called the adventitia.
The upper part of the esophagus has a special area of muscle at its beginning that relaxes to open the esophagus when it senses food or liquid coming toward it. This muscle is called the upper esophageal sphincter. The lower part of the esophagus that connects to the stomach is called the gastroesophageal junction, or GE junction. There is a special area of muscle near the GE junction called the lower esophageal sphincter. The lower esophageal sphincter controls the movement of food from the esophagus into the stomach and it keeps the stomach’s acid and digestive enzymes out of the esophagus.
The stomach has strong acid and enzymes that digest food. The epithelium or lining of the stomach is made of glandular cells that release acid, enzymes, and mucus. These cells have special features that protect them from the stomach’s acid and digestive enzymes.
In some people, acid can escape from the stomach into the esophagus. The medical term for the escape of acid from the stomach back into the esophagus is reflux or gastroesophageal reflux disease (GERD). In many cases, reflux can cause symptoms such as heartburn or a burning sensation radiating from the middle of the chest. However, in some cases, reflux can occur without any symptoms at all. If the reflux of stomach acid into the lower esophagus continues for a long time, the acid can cause injury to the lining of the esophagus, with abnormal glandular cells replacing the squamous cells that usually line the esophagus. These glandular cells usually look like the cells that line the stomach and are more resistant to stomach acid. When these glandular cells are noted in a person’s esophagus, he or she has a condition called Barrett esophagus. People with Barrett esophagus are at a highly increased risk for developing cancer of the esophagus (estimated at 30-100 x normal), and therefore need to be followed closely by their doctor. Even though they are at greater than average risk, most people with Barrett esophagus still do not go on to develop cancer of the esophagus.
There are 2 main types of esophageal cancer: squamous cell carcinoma and adenocarcinoma. Since the entire esophagus is normally lined with squamous cells, squamous cell carcinoma can occur anywhere along the length of the esophagus. At one time, squamous cell carcinoma was by far the more common of the 2 cancer types in the United States and was responsible for almost 90% of all esophageal cancers. Recently, this has changed. Now, squamous cell cancers make up less than 50% of esophageal cancers. .
Adenocarcinomas start in glandular tissue, which normally does not cover the esophagus. Before an adenocarcinoma can develop, glandular cells must replace an area of squamous cells, as in the case of Barrett esophagus. This occurs mainly in the lower esophagus, which is the site of most adenocarcinomas.