Causes and Symptoms The section of the gut from the esophageal sphincter in the upper stomach to the ileocecal valve at the end of the small intestine digests food taken into the body and absorbs its nutrients. This vital function also exposes the gut and its organs, the liver and pancreas, to ingested toxins that can initiate cancer and to materials that damage the gut lining, also potentially leading to cancer. Because diet greatly influences the chances for contracting these cancers, it is understandable that stomach cancer is the world’s most common type. Surprisingly, however, cancers of the small bowel are rare. Pancreatic cancer is the most lethal of these cancers and one of the most difficult to detect before irreversible damage has been done: Few patients live long after diagnosis. These facts and the large number of suspected carcinogens make the stomach and pancreatic cancers a pressing challenge for physicians and public health.
Broad similarities characterize the types of cancers throughout the upper gastrointestinal (GI) tract. The majority, adenocarcinomas, grow in and mimic gland tissue, but possible as well are cancers of the lymph tissue (lymphoma), hormone-secreting cells (carcinoid tumors), and the muscle wall of the bowel (sarcoma). Early symptoms tend to be vague and do not necessarily point specifically to cancer: abdominal pain, loss of appetite, weight loss, and perhaps diarrhea or vomiting.
While diet is a major factor in stomach cancer, its role in pancreatic and intestinal cancers is not as clear. A diet consisting mainly of pickled, smoked, or salted food with few fruits and vegetables, especially those containing vitamins A and C, is thought to be risky. In fact, countries with the highest rates of gastric cancer, such as Japan, are those that have long relied on such chemical preservation techniques rather than on refrigeration. It is probably no coincidence that the stomach cancer rate in the United States declined sharply after refrigeration became widespread in the 1930s; moreover, Japanese immigrants to the United States have sharply fewer gastric cancers than do their relatives in the homeland.
The presence of nitrites in the diet, alcohol consumption, radiation exposure, chronic gastritis (inflammation of the stomach lining), and cigarette smoking have also been suspected as gastric carcinogens. Hereditary susceptibility may sometimes play a role, although it is also possible that family members, living under the same conditions, are simply exposed to the same carcinogens and that no genetic susceptibility is involved. Finally, chronic stomach infection with the bacterium Helicobacter pylori has been linked to gastric cancer development.
Risk factors for the
pancreas and
small intestine are much less clear. Chronic pancreatitis, gallstones, and cirrhosis (scarring) of the liver pose some danger of initiating pancreatic cancer, and smokers and diabetics are twice as likely to develop it than are others. In March 2013, scientists at the Institute of Social and Preventive Medicine at the University of Zurich published a study of 450,000 subjects that found that consumption of processed meats increased the risk of premature death by cancer and other health problems. Chemists and others who work with organic solvents and petrochemicals also run a slightly higher risk. Intestinal cancer becomes more likely after the immune system has been damaged or late in the course of chronic intestinal diseases, such as Crohn’s disease and sprue.
Risky foods, diseases, or occupations do not inevitably lead to cancers. Tumor growth requires at least three factors: some agent that initiates a change in a cell’s genetic structure so that a new type of cell is created, called a
mutation; an agent that enhances the cell’s response to the initiator, encouraging it to reproduce; and the failure of the immune system to destroy the abnormal cells. Most small bowel and gastric cancers probably result from long-term overstimulation of the glands or mucosa. This overstimulation occurs when the body fights chemical irritants that have been ingested with food, drink, or air; the body’s defense mechanisms lead to inflammation in the damaged area. Chronic inflammation and continually stimulated cell division to repair damage eventually is likely to produce a mutated cell. If adapted to the harsh environment that produced it, the cell can multiply unchecked, overwhelm the immune system, and invade normal tissue; eventually, it may metastasize. A potentially lethal cancer can grow for months or years before its victim notices any definite changes in particular body functions or general health.
Eventually, however, danger signs begin. After initially complaining of abdominal pain, loss of appetite, and difficulty keeping food down, stomach cancer patients may have black, digested blood in the stool, weight loss, general weakness, bouts of vomiting blood, a swollen abdomen, a noticeable mass in the stomach, and iron-deficiency anemia. When the disease is well advanced, metastases become increasingly common, invading the lymph nodes, bile ducts, and liver and eventually spreading to the lungs, bones, and brain. The cancer becomes symptomatic relatively quickly. On average, patients go to their doctors about six months after noticing symptoms.
Pancreatic cancer is much less likely to cause early symptoms, and by the time patients seek medical help, the cancer is usually too far advanced to cure. Physicians suspect pancreatic adenocarcinoma when a patient complains of food aversion, progressive weight loss, and abdominal and back pain, especially when accompanied by vomiting, diarrhea, and jaundice. A rare form of pancreatic cancer (less than 5 percent of cancers in the pancreas) develops from the insulin-producing cells of the organ and makes abnormally high amounts of insulin; in this case, the symptoms are attributable to low blood sugar (hypoglycemia) and include weakness, loss of energy, dizziness, chills, muscle spasms, double vision, and, in extreme cases, coma.
Adenocarcinomas, lymphomas, carcinoid tumors, and sarcomas may form in the small bowel, and most of these grow slowly. Intestinal adenocarcinomas show up primarily in the jejunum or duodenum of elderly patients. Often, they first become apparent when they clog the bowel or bleed. Usually appearing in the stomach, lower jejunum, or ileum, lymphomas are suspected when the patient has fever, night sweats, weight loss, and abdominal pain. Intestinal carcinoid tumors may actively secrete hormones. If they metastasize, release of the hormones sometimes causes a bizarre group of symptoms that are collectively known as carcinoid syndrome: diarrhea, flushing, itching, low blood pressure, and heart disease. Intestinal sarcomas can occur anywhere in the small bowel and reveal themselves by bleeding.
Treatment and Therapy Since other diseases also cause the weight loss, abdominal pain, and nausea common to these cancers—for example, pancreatitis, malabsorption, inflammatory bowel disease, and gastritis—the diagnosis of cancer requires specific evidence from chemical tests, imaging, endoscopic procedures, or surgery. Suspecting stomach cancer, the physician may send the patient for an upper GI barium study. For this procedure, the patient drinks a mixture containing barium sulfate; the radio-opaque barium coats the stomach and under X-ray photography can be seen to outline a tumor if one is present. Tests to check for anemia and blood in the stool may also be ordered. If imaging and tests support a diagnosis of cancer, a gastroenterologist, inserting an endoscope through the patient’s mouth, will obtain biopsies of the tumor so that a pathologist can determine if the tumor is malignant. Since biopsies remove such small samples and can miss a cancerous portion of a tumor (especially a lymphoma or sarcoma), surgical biopsy may be necessary to settle the diagnosis beyond doubt.
Similarly, initial tests for pancreatic and intestinal cancer rely on imaging and chemical assays. A barium X-ray study of the small bowel, a computed tomography (CT) scan, or ultrasonography may locate the tumor. Again, endoscopic or surgical biopsy alone can verify the diagnosis of malignancy. Tumors in the small bowel usually lie beyond the reach of endoscopy, so when a barium study reveals a tumor, surgical biopsy is most often necessary to obtain tissue samples; at the same time, the tumor is usually removed to relieve or prevent obstruction of the bowel.
If a tumor has not spread and is well defined, cutting it out provides the best chance of a cure for cancers throughout the stomach, pancreas, and small bowel. Such surgeries are often technically difficult, however, because the patients are typically malnourished and weak and have difficulty enduring the rigors of surgery. When a stomach tumor is single and small, surgeons remove it and a small margin of tissue around its edges. Larger or multiple tumors force the removal of larger portions of the stomach and adjacent lymph nodes. For pancreatic cancer, if more than a single area of the pancreas is involved, the surgeon may remove the entire organ and, depending on the size and location of the tumor, parts of the duodenum and stomach as well. Cancers of the intestines are cut away along with a section of bowel, whose ends are then reconnected by suturing. Chemotherapy and radiation on their own have not proved reliable for shrinking stomach, pancreatic, and intestinal cancers (except lymphomas) and are usually used in conjunction with surgery, especially when a primary tumor has metastasized.
Sometimes endoscopic maneuvers can stop bleeding or relieve pain by clearing out obstructions or, in the case of an obstructed bile duct, by inserting a small perforated tube called a stent to ensure that bile and pancreatic juices flow freely. Pain management, whether with manipulative procedures or with drugs, becomes the primary focus of treatment when surgical cure for a cancer is unlikely. Surgeons do not attempt curative operations if the cancer has metastasized. At this point, surgery, if possible at all, is for relieving pain, preventing blockage, or minimizing blood loss.
Perspective and Prospects The frequency of these cancers and their distribution in the world vary considerably. Intestinal cancers make up less than 1 percent of all cancers and less than 5 percent of gastrointestinal cancers; pancreatic cancer accounts for only about 3 percent of all cancers. Yet the incidence of both cancers has been rising. In the United States, for example, pancreatic cancer increased about 25 percent from the 1950s to the 1990s. By 2002, it was the fourth leading cause of cancer death, and more than 30,000 Americans were diagnosed with the disease annually. At the same time, stomach cancer decreased dramatically, dropping from the United States’ most common cancer in the 1930s to about 2 percent of all cancers in the 1990s. Yet in Japan, Iceland, and parts of Central and South America and of Eastern Europe, the stomach cancer rate is very high, accounting for most of the nearly 700,000 new cases yearly. In 2008, the World Cancer Research Fund International listed stomach cancer as the fourth most common cancer in the world. Approximately 990,000 new cases of stomach cancer were diagnosed in 2008. The highest rates of stomach cancer are in Eastern Asia; specifically South Korea, Mongolia, and Japan. Worldwide, incidence of stomach cancer occur in men twice as often as women. In 2013, the American Cancer Society estimated that 21,600 cases of stomach cancer are diagnosed annually in the United States . In the United States, African Americans get these cancers more often than Caucasians. Probably because of their diet, poor people develop intestinal cancer more often than middle-class or upper-class people. The peak age group is fifty to fifty-nine years for stomach cancer and seventy to seventy-nine years for pancreatic and intestinal cancer.
The chances for successfully treating or drastically curtailing small bowel cancer are reasonably good; 20 percent of patients with adenocarcinomas in the small intestine survive for at least five years following diagnosis, and patients with carcinoid tumors have lived ten and even fifteen years after surgery. Treatment of small bowel or stomach lymphomas can result in a cure or prolonged survival in a significant percentage of cases. The prospects for pancreatic and stomach adenocarcinomas, however, are another story entirely. Overall, in the United States about 10 percent of gastric cancer patients are alive five years later. Pancreatic cancer is even deadlier, with 90 percent of patients dying in the first year after diagnosis, regardless of treatment. Of those with cancer of the pancreatic duct, only about 4 percent survive three years. Those with cancer in the insulin-producing cells fare better—a 30 percent survival rate—but this is a very rare type of cancer.
Because gastric cancer is common in Japan, doctors routinely screen patients for it by endoscopy or photofluorography (a type of X ray). Prescreening in Japan increases the overall survival rate of patients in the country. Many more cancers are caught early, while they are still surgically treatable. Endoscopic and chemical screenings for pancreatic cancer are also possible, but since the disease is so much less common, doctors do not perform the tests unless they already have good reason to suspect cancer. Avoidance of carcinogens, especially alcohol, remains the most promising way to escape gut cancers.
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