The esophagus is a hollow tube that connects the throat to the stomach. Figure 01 In an adult, the esophagus is approximately ten inches long and about an inch in diameter at its narrowest point. When a person swallows, muscles that line the walls of the esophagus contract, forcing food and liquid into the stomach. Glands in the esophagus produce mucus that lubricates this passageway and makes swallowing easier.
At either end of the esophagus are special muscular tissues called sphincters. The upper esophageal sphincter opens to allow food and liquid into the esophagus. The lower esophageal sphincter prevents stomach acid from backing up and causing irritation in the esophagus.
Esophageal cancer is divided into two major types—squamous cell carcinoma and adenocarcinoma—depending on the type of cells that have become cancerous. Figure 02 The walls of the esophagus are made up of several distinct layers. The inner lining of the esophagus is made up of thin, flat cells that resemble fish scales. These cells are called squamous cells, and cancer that begins in this tissue is called squamous cell carcinoma. Glandular cells that secrete mucus are found in a layer deeper in the wall of the esophagus. When these cells become malignant, the cancer is called adenocarcinoma.
Squamous cell carcinomas generally develop in the upper or middle sections of the esophagus. Adenocarcinomas generally develop is the lower sections of the esophagus.
The number of cases of esophageal cancer is rising in the U.S. For the year 2001, the American Cancer Society estimates that 13,200 new cases will be diagnosed, and 12,500 people will die from the disease. Although treatments for esophageal cancer are available, the disease is rarely curable, with the overall 5-year survival rate ranging from 5% to 25%.
Figure 01. The esophagus
Figure 02. The esophagus wall
The underlying cause of esophageal cancer is not well understood. Several factors, such as smoking and alcohol abuse, have been linked with a higher risk of squamous cell carcinoma of the esophagus, but the exact mechanism by which these risk factors result in cancer is not known. Many scientists believe that alcohol or chemicals in tobacco smoke damage the DNA in the cells lining the esophagus, and it is these mutations that leads to the uncontrolled cell growth characteristic of cancer.
Long-term irritation to the esophagus, such as that caused by gastroesophageal reflux disease (GERD), can also lead to adenocarcinoma of the esophagus. Almost everyone with adenocarcinoma first has a condition called Barrett's esophagus. This condition is caused by excess esophageal exposure to stomach acid. People who have severe GERD symptoms for many years have a higher risk of Barrett's, especially if they smoke and drink excessively.
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