What is cancer of the esophagus?

To understand esophagus cancer, it helps to know about the normal structure and function of the esophagus.

The esophagus

The esophagus is a hollow, muscular tube that connects the throat to the stomach. It lies behind the trachea (windpipe) and in front of the spine.

Food and liquids that are swallowed travel through the inside of the esophagus (called the lumen) to reach the stomach. In adults, the esophagus is usually between 10 and 13 inches long and is about ¾ of an inch across at its smallest point.

The wall of the esophagus has several layers. These layers are important for understanding where cancers in the esophagus tend to start and how they may grow.

Mucosa: This is the layer that lines the inside of the esophagus. The mucosa has 3 parts:

• The epithelium forms the innermost lining of the esophagus and is normally made up of flat, thin cells called squamous cells. This is where most cancers of the esophagus start.
• The lamina propria is a thin layer of connective tissue right under the epithelium.
• The muscularis mucosa is a very thin layer of muscle under the lamina propria.

Submucosa: This is a layer of connective tissue just below the mucosa that contains blood vessels and nerves. In some parts of the esophagus, this layer also contains glands that secrete mucus.

Muscularis propria: This is a thick band of muscle under the submucosa. This layer of muscle contracts in a coordinated, rhythmic way to push food along the esophagus from the throat to the stomach.

Adventitia: This is the outermost layer of the esophagus, which is formed by connective tissue.

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 (GE) junction. A special area of muscle near the GE junction, called 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.

Reflux and Barrett's esophagus

The stomach has strong acid and enzymes that digest food. The epithelium (inner lining) of the stomach is made of gland 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 escapes from the stomach back into the esophagus. The medical term for this is gastroesophageal reflux disease (GERD), or just reflux. In many cases, reflux can cause symptoms such as heartburn or a burning feeling spreading out from the middle of the chest. But sometimes, reflux can occur without any symptoms at all.

If reflux of stomach acid into the lower esophagus continues for a long time, it can damage the lining of the esophagus. This causes the squamous cells that usually line the esophagus to be replaced with gland cells. These gland cells usually look like the cells that line the stomach and the small intestine and are more resistant to stomach acid. The presence of gland cells in the esophagus is known as Barrett's (or Barrett) esophagus.

People with Barrett's esophagus are much more likely to develop cancer of the esophagus. These people require close medical follow-up in order to find cancer early. Still, although they have a higher risk, most people with Barrett's esophagus do not go on to develop cancer of the esophagus.

Esophageal cancer

Cancer of the esophagus (also referred to as esophageal cancer) starts in the inner layer (the mucosa) and grows outward (through the submucosa and the muscle layer). Since 2 types of cells can line the esophagus, there are 2 main types of esophageal cancer: squamous cell carcinoma and adenocarcinoma.

The esophagus is normally lined with squamous cells. The cancer starting in these cells is called squamous cell carcinoma. This type of cancer can occur anywhere along the esophagus. At one time, squamous cell carcinoma was by far the more common type of esophageal cancer in the United States. This has changed over time, and now it makes up less than half of esophageal cancers in this country.

Cancers that start in gland cells are called adenocarcinomas. This type of cell is not normally part of the inner lining of the esophagus. Before an adenocarcinoma can develop, gland cells must replace an area of squamous cells, which is what happens in Barrett's esophagus. This occurs mainly in the lower esophagus, which is the site of most adenocarcinomas.

Cancers that start at the area where the esophagus joins the stomach (the GE junction), which includes about the first 2 inches of the stomach (called the cardia), tend to behave like esophagus cancers (and are treated like them, as well), so they are grouped with esophagus cancers.