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Colon Cancer

Colon Cancer

The colon is the part of the digestive system where the waste material is stored. The rectum is the end of the colon adjacent to the anus. Together, they form a long, muscular tube called the large intestine (also known as the large bowel). Tumors of the colon and rectum are growths arising from the inner wall of the large intestine. Benign tumors of the large intestine are called polyps. Malignant tumors of the large intestine are called cancers.

 

Benign polyps do not invade nearby tissue or spread to other parts of the body. Benign polyps can be easily removed during colonoscopy and are not life-threatening.

 

If benign polyps are not removed from the large intestine, they can become malignant (cancerous) over time. Most of the cancers of the large intestine are believed to have developed from polyps. Cancer of the colon and rectum (also referred to as colorectal cancer) can invade and damage adjacent tissues and organs. Cancer cells can also break away and spread to other parts of the body (such as liver and lung) where new tumors form.

 

The spread of colon cancer to distant organs is called metastasis of the colon cancer. Once metastasis has occurred in colorectal cancer, a complete cure of the cancer is unlikely.

 

Globally, cancer of the colon and rectum is the third leading cause of cancer in males and the fourth leading cause of cancer in females. The frequency of colorectal cancer varies around the world. It is common in the Western world and is rare in Asia and Africa. In countries where the people have adopted western diets, the incidence of colorectal cancer is increasing.

Symptoms

Symptoms of colon cancer are numerous and nonspecific. They include fatigue, weakness, shortness of breath, change in bowel habits, narrow stools, diarrhea or constipation, red or dark blood in stool, weight loss, abdominal pain, cramps, or bloating. Other conditions such as irritable bowel syndrome (spastic colon), ulcerative colitisCrohn's disease, diverticulosis, and peptic ulcer disease can have symptoms that mimic colorectal cancer.

 

For more information on these conditions, please read the following articles: Irritable Bowel Syndrome, Ulcerative ColitisCrohn's DiseaseDiverticulosis, and Peptic Ulcer Disease.

 

Colon cancer can be present for several years before symptoms develop. Symptoms vary according to where in the large bowel the tumor is located. The right colon is spacious, and cancers of the right colon can grow to large sizes before they cause any abdominal symptoms. Typically, right-sided cancers cause iron deficiency anemia due to the slow loss of blood over a long period of time. Iron deficiency anemia causes fatigue, weakness, and shortness of breath.

 

The left colon is narrower than the right colon. Therefore, cancers of the left colon are more likely to cause partial or complete bowel obstruction. Cancers causing partial bowel obstruction can cause symptoms of constipation, narrowed stool, diarrhea, abdominal pains, cramps, and bloating. Bright red blood in the stool may also indicate a growth near the end of the left colon or rectum.

Causes

Doctors are certain that colorectal cancer is not contagious (a person cannot catch the disease from a cancer patient). Some people are more likely to develop colorectal cancer than others. Factors that increase a person's risk of colorectal cancer include high fat intake, a family history of colorectal cancer and polyps, the presence of polyps in the large intestine, and chronic ulcerative colitis.

 

Diet and colon cancer

Diets high in fat are believed to predispose humans to colorectal cancer. In countries with high colorectal cancer rates, the fat intake by the population is much higher than in countries with low cancer rates. It is believed that the breakdown products of fat metabolism lead to the formation of cancer-causing chemicals (carcinogens). Diets high in vegetables and high-fiber foods such as whole-grain breads and cereals may rid the bowel of these carcinogens and help reduce the risk of cancer.

 

Colon polyps and colon cancer

Doctors believe that most colon cancers develop in colon polyps. Therefore, removing benign colon polyps can prevent colorectal cancer. Colon polyps develop when chromosome damage occurs in cells of the inner lining of the colon. Chromosomes contain genetic information inherited from each parent. Normally, healthy chromosomes control the growth of cells in an orderly manner.

 

When chromosomes are damaged, cell growth becomes uncontrolled, resulting in masses of extra tissue (polyps). Colon polyps are initially benign. Over years, benign colon polyps can acquire additional chromosome damage to become cancerous.

 

Ulcerative colitis and colon cancer

Chronic ulcerative colitis causes inflammation of the inner lining of the colon. For further information, please read the Ulcerative Colitis article. Colon cancer is a recognized complication of chronic ulcerative colitis. The risk for cancer begins to rise after eight to 10 years of colitis. The risk of developing colon cancer in a patient with ulcerative colitis also is related to the location and the extent of his or her disease.

 

Current estimates of the cumulative incidence of colon cancer associated with ulcerative colitis are 2.5% at 10 years, 7.6% at 30 years, and 10.8% at 50 years. Patients at higher risk of cancer are those with a family history of colon cancer, a long duration of colitis, extensive colon involvement, and those with primary sclerosing cholangitis (PSC).

 

Since the cancers associated with ulcerative colitis have a more favorable outcome when caught at an earlier stage, yearly examinations of the colon often are recommended after eight years of known extensive disease. During these examinations, samples of tissue (biopsies) can be taken to search for precancerous changes in the lining cells of the colon. When precancerous changes are found, removal of the colon may be necessary to prevent colon cancer.

 

Genetics and colon cancer

A person's genetic background is an important factor in colon cancer risk. Among first-degree relatives of colon cancer patients, the lifetime risk of developing colon cancer is 18% (a threefold increase over the general population in the United States).

 

Even though family history of colon cancer is an important risk factor, majority (80%) of colon cancers occur sporadically in patients with no family history of colon cancer. Approximately 20% of cancers are associated with a family history of colon cancer. And 5 % of colon cancers are due to hereditary colon cancer syndromes. Hereditary colon caner syndromes are disorders where affected family members have inherited cancer-causing genetic defects from one or both of the parents.

 

Chromosomes contain genetic information, and chromosome damages cause genetic defects that lead to the formation of colon polyps and later colon cancer. In sporadic polyps and cancers (polyps and cancers that develop in the absence of family history), the chromosome damages are acquired (develop in a cell during adult life).

 

The damaged chromosomes can only be found in the polyps and the cancers that develop from that cell. But in hereditary colon cancer syndromes, the chromosome defects are inherited at birth and are present in every cell in the body. Patients who have inherited the hereditary colon cancer syndrome genes are at risk of developing large number of colon polyps, usually at young ages, and are at very high risk of developing colon cancer early in life, and also are at risk of developing cancers in other organs.

 

FAP (familial adenomatous polyposis) is a hereditary colon cancer syndrome where the affected family members will develop countless numbers (hundreds, sometimes thousands) of colon polyps starting during the teens. Unless the condition is detected and treated (treatment involves removal of the colon) early, a person affected by familial polyposis syndrome is almost sure to develop colon cancer from these polyps.

 

Cancers usually develop in the 40s. These patients are also at risk of developing other cancers such as cancers in the thyroid gland, stomach, and the ampulla (the part where the bile ducts drain into the duodenum just beyond the stomach).

 

AFAP (attenuated familial adenomatous polyposis) is a milder version of FAP. Affected members develop less than 100 colon polyps. Nevertheless, they are still at very high risk of developing colon cancers at young ages. They are also at risk of having gastric polyps and duodenal polyps.

 

HNPCC (hereditary nonpolyposis colon cancer) is a hereditary colon cancer syndrome where affected family members can develop colon polyps and cancers, usually in the right colon, in their 30s to 40s.

 

Certain HNPCC patients are also at risk of developing uterine cancer, stomach cancerovarian cancer, and cancers of the ureters (the tubes that connect the kidneys to the bladder), and the biliary tract (the ducts that drain bile from the liver to the intestines).

 

MYH polyposis syndrome is a recently discovered hereditary colon cancer syndrome. Affected members typically develop 10-100 polyps occurring at around 40 years of age, and are at high risk of developing colon cancer.

Treatment

Surgery is the most common treatment for colorectal cancer. During surgery, the tumor, a small margin of the surrounding healthy bowel, and adjacent lymph nodes are removed. The surgeon then reconnects the healthy sections of the bowel. In patients with rectal cancer, the rectum is permanently removed.

 

The surgeon then creates an opening (colostomy) on the abdomen wall through which solid waste in the colon is excreted. Specially trained nurses (enterostomal therapists) can help patients adjust to colostomies, and most patients with colostomies return to a normal lifestyle.

 

The long-term prognosis after surgery depends on whether the cancer has spread to other organs (metastasis). The risk of metastasis is proportional to the depth of penetration of the cancer into the bowel wall. In patients with early colon cancer which is limited to the superficial layer of the bowel wall, surgery is often the only treatment needed.

 

These patients can experience long-term survival in excess of 80%. In patients with advanced colon cancer, wherein the tumor has penetrated beyond the bowel wall and there is evidence of metastasis to distant organs, the five-year survival rate is less than 10%.

 

In some patients, there is no evidence of distant metastasis at the time of surgery, but the cancer has penetrated deeply into the colon wall or reached adjacent lymph nodes. These patients are at risk of tumor recurrence either locally or in distant organs. Chemotherapy in these patients may delay tumor recurrence and improve survival.

 

Chemotherapy is the use of medications to kill cancer cells. It is a systemic therapy, meaning that the medication travels throughout the body to destroy cancer cells. After colon cancer surgery, some patients may harbor microscopic metastasis (small foci of cancer cells that cannot be detected). Chemotherapy is given shortly after surgery to destroy these microscopic cells.

 

Chemotherapy given in this manner is called adjuvant chemotherapy. Recent studies have shown increased survival and delay of tumor recurrence in some patients treated with adjuvant chemotherapy within five weeks of surgery. Most drug regimens have included the use of 5-flourauracil (5-FU). On the other hand, chemotherapy for shrinking or controlling the growth of metastatic tumors has been disappointing. Improvement in the overall survival for patients with widespread metastasis has not been convincingly demonstrated.

 

Chemotherapy is usually given in a doctor's office, in the hospital as a outpatient, or at home. Chemotherapy is usually given in cycles of treatment periods followed by recovery periods. Side effects of chemotherapy vary from person to person, and also depend on the agents given.

 

Modern chemotherapy agents are usually well tolerated, and side effects are manageable. In general, anticancer medications destroy cells that are rapidly growing and dividing.

 

Therefore, red blood cells, platelets, and white blood cells are frequently affected by chemotherapy. Common side effects include anemia, loss of energy, easy bruising, and a low resistance to infections. Cells in the hair roots and intestines also divide rapidly. Therefore, chemotherapy can cause hair loss, mouth sores, nausea, vomiting, and diarrhea.

 

Radiation therapy in colorectal cancer has been limited to treating cancer of the rectum. There is a decreased local recurrence of rectal cancer in patients receiving radiation either prior to or after surgery. Without radiation, the risk of rectal cancer recurrence is close to 50%. With radiation, the risk is lowered to approximately 7%. Side effects of radiation treatment include fatigue, temporary or permanent pelvic hair loss, and skin irritation in the treated areas.

 

Other treatments have included the use of localized infusion of chemotherapeutic agents into the liver, the most common site of metastasis. This involves the insertion of a pump into the blood supply of the liver which can deliver high doses of medicine directly to the liver tumor. Response rates for these treatments have been reported to be as high as eighty percent. Side effects, however, can be serious. Additional experimental agents considered for the treatment of colon cancer include the use of cancer-seeking antibodies bound to cancer-fighting drugs.

 

Such combinations can specifically seek and destroy tumor tissues in the body. Other treatments attempt to boost the immune system, the bodies' own defense system, in an effort to more effectively attack and control colon cancer. In patients who are poor surgical risks, but who have large tumors which are causing obstruction or bleeding, laser treatment can be used to destroy cancerous tissue and relieve associated symptoms. Still other experimental agents include the use of photodynamic therapy. In this treatment, a light sensitive agent is taken up by the tumor which can then be activated to cause tumor destruction.

 

A person's genetic background is an important factor in colon cancer risk. Among first-degree relatives of colon cancer patients, the lifetime risk of developing colon cancer is 18% (a threefold increase over the general population in the United States).

 

Even though family history of colon cancer is an important risk factor, majority (80%) of colon cancers occur sporadically in patients with no family history of colon cancer. Approximately 20% of cancers are associated with a family history of colon cancer. And 5 % of colon cancers are due to hereditary colon cancer syndromes. Hereditary colon caner syndromes are disorders where affected family members have inherited cancer-causing genetic defects from one or both of the parents.

 

Chromosomes contain genetic information, and chromosome damages cause genetic defects that lead to the formation of colon polyps and later colon cancer. In sporadic polyps and cancers (polyps and cancers that develop in the absence of family history), the chromosome damages are acquired (develop in a cell during adult life).

 

The damaged chromosomes can only be found in the polyps and the cancers that develop from that cell. But in hereditary colon cancer syndromes, the chromosome defects are inherited at birth and are present in every cell in the body. Patients who have inherited the hereditary colon cancer syndrome genes are at risk of developing large number of colon polyps, usually at young ages, and are at very high risk of developing colon cancer early in life, and also are at risk of developing cancers in other organs.

 

FAP (familial adenomatous polyposis) is a hereditary colon cancer syndrome where the affected family members will develop countless numbers (hundreds, sometimes thousands) of colon polyps starting during the teens. Unless the condition is detected and treated (treatment involves removal of the colon) early, a person affected by familial polyposis syndrome is almost sure to develop colon cancer from these polyps.

 

Cancers usually develop in the 40s. These patients are also at risk of developing other cancers such as cancers in the thyroid gland, stomach, and the ampulla (the part where the bile ducts drain into the duodenum just beyond the stomach).

 

AFAP (attenuated familial adenomatous polyposis) is a milder version of FAP. Affected members develop less than 100 colon polyps. Nevertheless, they are still at very high risk of developing colon cancers at young ages. They are also at risk of having gastric polyps and duodenal polyps.

 

HNPCC (hereditary nonpolyposis colon cancer) is a hereditary colon cancer syndrome where affected family members can develop colon polyps and cancers, usually in the right colon, in their 30s to 40s. Certain HNPCC patients are also at risk of developing uterine cancer, stomach cancer, ovarian cancer, and cancers of the ureters (the tubes that connect the kidneys to the bladder), and the biliary tract (the ducts that drain bile from the liver to the intestines).

 

MYH polyposis syndrome is a recently discovered hereditary colon cancer syndrome. Affected members typically develop 10-100 polyps occurring at around 40 years of age, and are at high risk of developing colon cancer.

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