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Asbestos: Selected Cancers
FIGURE 9.1 Anatomy of the esophagus, colon, rectum, and other digestive organs.
SOURCE: Copyright 2005 American Cancer Society, Inc. Reprinted with permission from www.cancer.org.
The incidence of carcinoma of the esophagus varies widely among countries. In regions extending from Iran through the steppes of Central Asia, Mongolia, and the northern portion of China, cancer frequencies are 10-100 times higher than in the countries at lowest risk. Squamous-cell carcinoma still predominates in the areas of high endemic risk, whereas adenocarcinoma now makes up about 50% of all cases in the low-risk areas of the United States, Europe, South Africa, Southeast Asia, and Japan.
The known risk factors differ somewhat for the two major histologic types of esophageal cancer. Known risk factors for squamous-cell carcinoma include all forms of tobacco-smoking (cigarettes, cigars, pipes, and bidis), use of chewing tobacco or snuff, and excessive consumption of alcohol. The combination of tobacco use and alcohol consumption potentiates the risk of either factor alone. Factors known to increase the risk of adenocarcinoma include chronic esophageal reflux (regurgitation of stomach acid and bile through the lower esophageal sphincter into the lower esophagus), obesity (which contributes to reflux), smoking, and achalasia (a type of esophageal dysfunction).
Adenocarcinoma of the esophagus develops from Barrett’s esophagus, a premalignant condition in which normal squamous epithelium of the lower esophagus is replaced with metaplastic columnar epithelium. The main cause of Barrett’s esophagus is thought to be chronic gastroesoph-