Gastrointestinal (GI) cancers include cancer of the esophagus, stomach, small intestine, colon, rectum, and anus as well as cancers of the liver, pancreas, gallbladder, and biliary system.
The GI tract, or digestive tract, starts from the oral cavity (mouth) and proceeds to the esophagus, the stomach, the duodenum, the small intestine, the large intestine (colon and rectum), and the anus. It processes all the food consumed. Along the way through the tract, food is digested, nutrients and water are extracted, and waste is eliminated from the body in the form of stool and urine. Cancer can affect any of the gastrointestinal organs. The National Cancer Institute estimates that 25% of all cancers are gastrointestinal, with the majority of these occurring in the colon and rectum (colorectal cancers). The next sites most commonly affected by GI cancers are the pancreas, stomach, liver, and esophagus. A brief overview of GI cancers follows; the reader should refer to other specific encyclopedia entries shown in bold for more comprehensive information on these cancers and their treatment. The reader should also note that the overview below does not discuss oral cavity cancers. Those cancers are also discussed in individual entries.
Types of cancers
The esophagus is a muscular, hollow tube that carries food from the oropharynx (area behind mouth and soft palate) to the stomach. It consists of several layers. Esophageal cancer usually develops in the inner layer cells and grows outward. There are two major types of esophageal cancer. The first occurs in the cells found in the lining of the esophagus (squamous cells), and the cancer is called squamous cell carcinoma. It can develop anywhere along the entire length of the esophagus and represents approximately half of all reported esophageal cancers. The second type of cancer known to occur in the esophagus is an adenocarcinoma, which is cancer of the glandular cells that line the inside of organs. Adenocarcinoma occurs near the stomach entrance and may be associated with a condition known as Barrett's esophagus . This is a disorder in which the lining of the esophagus undergoes cellular changes as a result of chronic irritation and inflammation resulting from a backwash of acidic stomach gastric juices. Esophageal adenocarcinomas cannot develop unless squamous cells have been transformed by the acid reflux of the stomach juices. The American Cancer Society (ACS) predicted the occurrence of approximately 12, 300 new cases of esophageal cancer in 2000 which will result in some 12, 100 deaths in the United States.
Stomach cancer is also called gastric cancer. The stomach is located in the upper abdomen under the ribs. It is the most expandable organ of the digestive system. Food reaches the stomach from the esophagus and is broken down by gastric juices secreted by the stomach. After leaving the stomach, partially broken down food passes into the small intestine and afterwards into the colon (first part of the large intestine). In cancer of the stomach, cancerous cells are found in the tissues of the stomach and this cancer can develop anywhere in the organ. It may grow along the stomach wall into other organs such as the esophagus or small intestine. Or it may go through the stomach wall and invade the nearby lymph nodes or organs such as the liver, pancreas, and colon. And it may also spread to more distant organs, such as the lungs, the lymph nodes located above the collar bone, and the ovaries. The major type of stomach cancer is adenocarcinoma (90%). Approximately 24, 000 new cases of stomach cancer are diagnosed per year in the US. The number of cases, as well as the death rate, have declined significantly over the past several decades, but it is still the seventh leading cause of cancer deaths. A cure is possible if the cancer is found before spreading to other organs. Unfortunately, the early symptoms are not very noticeable, and by the time stomach cancer is diagnosed, it has in many cases already metastasized.
The liver is one of the largest organs in the body. In normal adults, it weighs about three pounds and is located in the upper right side of the abdomen, under the right lung and rib cage. It plays a major role in digestion, in the transformation of food into energy and in filtering and storing blood. It is also responsible for processing nutrients and drugs, producing bile, controlling the level of glucose (sugar) in the blood, detoxifying blood, and regulating blood clotting. In cancer of the liver, cancerous cells are found in the tissues of the liver. Primary liver cancer is cancer that starts in the liver. As such, it is different from cancer that starts somewhere else and spreads to the liver. Liver cancer is a rare form of GI cancer in the United States with only about 15, 000 new cases diagnosed in 2000. Primary cancers of the liver and of the bile ducts are far more common in Africa and Asia than in America, where they only represent 1.5% of all cancer cases. The highest occurrence rate is in Vietnamese men (41.8 per 100, 000), probably a result of the high incidence of viral hepatitis infections in their country. Asian-American groups also have higher liver cancer incidence rates than the Caucasian population. Liver cancer mortality rates calculated for populations for which statistics are available are highest in China.
There are four main types of liver cancer: angiosarcoma, a rare type of cancer that starts in the blood vessels of the liver; hepatoblastoma, another rare type of liver cancer occurring chiefly in young children; cholangiocarcinoma, which starts in the bile ducts and accounts for approximately 13% of liver cancers; and finally, hepatocellular carcinoma, also known as hepatoma. The most common liver cancer is hepatocellular carcinoma which accounts for approximately 84% of liver cancers. As is the case with stomach cancer, liver cancer is hard to diagnose early because there are seldom any clear-cut symptoms.
|Esophageal cancer||Squamous cell carcinoma|
|Hepatocellular carcinoma (hepatoma)|
|Squamous cell carcinoma|
|Small cell (oat cell) carcinoma|
|Acinar cell carcinoma|
|Gastroinstestinal stromal tumors|
|Anal cancer||Squamous cell carcinoma|
|Basal cell carcinoma|
However, some diseases have been identified as liable to increase a person's risk of getting liver cancer. They include: hepatitis B, hepatitis C, cirrhosis of the liver, exposure to certain chemicals such as aflatoxin (a substance made by a fungus in tropical regions and that can infect wheat, peanuts, soybeans, corn, and rice), vinyl chloride, thorium dioxide, anabolic steroids, arsenic, and birth control pills (of a type no longer prescribed).
The gallbladder is a pear-shaped organ located just under the liver in the upper abdomen. Its role in digestion is to store and release the bile produced by the liver into the stomach to help break down fat. In gallbladder cancer , the cancer cells develop in the tissues of the gall-bladder. Several types of cancer can occur, such as adenocarcinoma, squamous cell carcinoma, carcinosarcoma and small cell (oat cell) carcinoma, all of them uncommon. Approximately 6, 000 to 7, 000 new cases are diagnosed per year in the U. S., affecting women twice as often as men and occurring mostly in the elderly.
The pancreas is a tongue-shaped glandular organ lying below and behind the stomach. It consists of two areas, the exocrine and endocrine regions. The endocrine pancreas secretes the hormones insulin and glucagon, which regulate blood sugar. The exocrine pancreas secretes pancreatic juice into the small intestine. The juice contains enzymes that break down fats and proteins so that the body can use them. In pancreatic cancer, the cancer can develop either in the cells that secrete the pancreatic juice (exocrine pancreatic cancer) or in the cells that release the hormones (endocrine pancreatic cancer). Exocrine pancreatic cancer is much more common than endocrine. Several types can develop, the majority being various types of carcinomas. The American Cancer Society predicted that, in 2000, about 28, 300 people in the U. S. will be diagnosed with this type of cancer and that approximately 28, 200 will die of the disease. Pancreatic cancer is the fourth leading cause of cancer death in men and women. Because the pancreas is located deep inside the body, it cannot be felt during a routine physical exam, and no tests are presently available to allow early detection.
The colon, the first part of the large intestine, extends from the end of the small intestine to the rectum. The colon has four major divisions. The first is called the ascending colon, it starts where the small intestine attaches and extends upward on the right side of the abdomen. The second part is the transverse colon and it extends across the body to the left side where it joins the third section, called the descending colon, which continues downward on the left side. The fourth part of the colon is the sigmoid colon, which joins the rectum. The rectum joins the anus, where stool passes out of the body.
Each of the divisions of the colon and rectum has several layers of tissue. Colorectal cancers usually start in the innermost layer and can grow through some or all of the other layers. Colorectal cancers are common, and occur more frequently in people over the age of 50. The ACS estimated that in 2001 in the U. S., about 46, 000 new cases of colon cancer will be diagnosed in men, and about 52, 000 cases in women. For rectal cancers, the ACS estimates that about 21, 000 men and 16, 000 women will be diagnosed in 2001. The number of new colorectal cancer cases and reported deaths have declined in recent years due to improved screening and diagnostic methods. Colorectal cancers are highly treatable when detected early, but the symptoms are often not obvious in early stages.
Over 95% of colorectal cancers are adenocarcinomas. Other, less common types of colorectal cancers are: carcinoid tumors, which develop from the hormone-producing cells of the intestine, gastrointestinal stromal tumors, which start in the connective tissue and muscle layers located in the wall of the colon and rectum, and lymphomas, which are cancers of the immune system cells that usually occur in the lymph nodes but may also start in the colon.
The anus has several types of tissues. Each type of tissue also contains several types of cells and cancer can develop in each of these kinds of tissues. Approximately half are squamous cell carcinomas. This type of cancer is found in the surface cells that line the anus and most of the anal canal. Another 15% of anal cancers consist of adenocarcinomas and usually start in glands found in the anus area. The remaining anal cancers are accounted for by basal cell carcinomas and malignant melanomas. Anal cancer is usually diagnosed in people over 50. People who have the human papillomavirus (HPV) also have a greater chance of developing anal cancer as well as men who practice anal sex. How treatable the cancer is depends partly on where it starts.
See Also Bile duct cancer; Carcinoid tumors, gastrointestinal; Human papilloma virus; Laryngeal cancer; Liver cancer, primary; Melanoma; Pancreatic cancer, endocrine; Pancreatic cancer, exocrine; Small intestinal cancer; Upper gastrointestinal endoscopy
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Monique Laberge, Ph.D.
—A part of the body which lies between the thorax and the pelvis. It contains a cavity (abdominal cavity) which holds organs such as the pancreas, stomach, intestines, liver, gallbladder. It is enclosed by the abdominal muscles and the vertebral column (backbone).
—A greenish-yellow fluid produced by the liver and stored in the gallbladder.
—Passages external to the liver for the transport of bile.
—The conversion of food in the stomach and in the intestines into substances capable of being absorbed by the blood.
—Organs and paths responsible for processing food in the body. These are the mouth, the esophagus, the stomach, the liver, the gallbladder, the pancreas, the small intestine, the colon and the rectum.
—An acidic secretion of the stomach that breaks down the proteins contained in the ingested food, prior to digestion.
—An organ that produces and releases substances for use in the body, such as fluids or hormones.
—Small, bean-shaped organs surrounded by a capsule of connective tissue. Also called lymph glands. Lymph nodes are spread out along lymphatic vessels and store special cells (lymphocytes), which filter the lymphatic fluid (lymph).
—The tissues and organs that produce, store, and carry white blood cells that fight infection. It includes the bone marrow, spleen, thymus, and lymph nodes as well as a network of thin vessels (lymphatic vessels) that carry lymph and white blood cells into all the tissues of the body.
—The transfer of cancer from one location or organ to another one not directly related to it.
—One of two small oval-shaped organs located on either side of the uterus. They are female reproductive glands in which the ova (eggs) are formed.
—The part of the digestive tract located between the stomach and the large intestine.
—Flat, thin cells, such as found on the outer layer of the skin.
—The extent to which a cancer has spread from its original site to other parts of the body. A Stage 1 cancer is less advanced than a Stage 4 cancer.