Nature Of This Cancer Type

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The esophagus is a muscular tube that carries food and liquid from the mouth to the stomach (Figures 7.1 and 9.1).

The American Cancer Society (Jemal et al. 2006) has estimated that 14,550 new cases of and 13,770 deaths from esophageal cancer (ICD-9 150; ICD-O-3 C15.0-15.9) will occur in the United States in 2006. Esophageal cancer ranks 19th in numbers of cases of cancer in the United States and sixth in developing countries (Kleihues and Stewart 2003).

The incidence is nearly 4 times higher in men than in women in the United States and slightly higher among blacks than among whites. The incidence has increased among men by an average of 1.7% per year since 1975, although the predominant histologic type and location of cancers in the esophagus have changed since the 1970s in most economically developed countries. Historically, the most common form of esophageal cancer worldwide was squamous-cell carcinoma, which occurred largely in the upper two-thirds of the esophagus (Blot 1994). Since the 1970s, the incidence of adenocarcinoma of the lower one-third of the esophagus and the junction with the stomach has increased by a factor of more than 5 among white and black men in the United States, whereas the incidence of squamous-cell carcinoma has decreased moderately. Rates of adenocarci-noma are also rising in women but are much lower than in men. Adenocar-cinoma now makes up more than half of the esophageal cancers in white males, whereas squamous-cell carcinoma remains the predominant histo-logic type among black people and in high-incidence populations worldwide (Blot and McLaughlin 1999).

Gallbladde

Rectum

Colon

Live

Gallbladde

Rectum

Colon

Live

Esophagus

Stomach

Small Intestine

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.

Esophagus

Stomach

Small Intestine

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 10100 times higher than in the countries at lowest risk. Squamous-cell carcinoma still predominates in the areas of high endemic risk, whereas adeno-carcinoma 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 adeno-carcinoma 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-

ageal reflux. People with Barrett's esophagus are at increased risk for developing cancer of the esophagus and should be followed closely by their doctors. Even though they are at greater than average risk, most people with Barrett's esophagus do not develop cancer of the esophagus.

EPIDEMIOLOGIC EVIDENCE CONSIDERED Cohort Studies

The cohorts that presented usable information on the risk of esophageal cancer were indicated in Table 6.1. Their histories and design properties are described in Table B.1, and the details of their results concerning cancer at this site are abstracted in Table D.3. The results of both the cohort and case-control studies are summarized in Table 9.1, and Figures 9.2 and 9.3 are plots of relative risks (RRs) for overall exposure and for exposure-response gradients from the cohort studies reviewed.

TABLE 9.1 Summary of Epidemiologic Findings Regarding Cancer of Esophagus

Study Type

Figure

Populations Included

(95% CI)

Between-Study SD

Cohort

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