Colon cancer is the third most common cancer and the third leading cause of cancer-related death among both men and women. However, it is among the most treatable cancers when diagnosed and treated in its early stages. The five-year survival rate among those diagnosed and treated at an early stage is 90%. In some cases, regular screening enables the detection of possible precancerous formations and thus prevents the formation of cancer in the first place.
Although colon cancer is seen all over the world, it is more common in industrialized countries such as the USA, Canada, Australia, New Zealand and Western Europe. It is common. The countries with the lowest incidence of colon cancer are developing countries in Africa and Asia.
Cancer occurs as a result of uncontrolled growth of cells, disrupting the normal balance of dying damaged or aged cells and being replaced by new ones. Most colon cancers develop from polyps, formations protruding from the mucosa covering the inner surface of the intestine. In parallel with age, polyps are common, especially over the age of 50. While most polyps remain benign, adenomatous type polyps may turn into cancer over time. Scientists have identified a series of genetic changes in the DNA of the cells lining the inside of the colon that lead to the formation of polyps and subsequently colon cancer. There are also hereditary types of colon cancer, but most of the genetic changes depend on age and various environmental factors.
Risk Factors
It is not known exactly why colon cancer occurs. Some people carry genes that predispose them to certain types of cancer, such as colon cancer. It is thought that some cancers occur as a result of damage to the cells carrying these genes due to environmental factors such as toxins or factors such as nutrition and smoking.
Age is an important risk factor. The main risk factors for colon cancer are age, individual or family history of cancer, lifestyle and nutrition. The risk of colon cancer increases with age, with more than 90% of diagnosed patients being over 50 years old. Genetic factors or chronic If inflammatory bowel disease is not present, colon cancer affects young people less. Colon cancers are thought to develop from adenomatous type polyps over a period of seven to ten years. It is estimated that approximately 15% of colon cancers are hereditary. Having a family history of colon cancer increases the risk. The risk is higher if the age at which colon cancer occurs in the family is at an early age. Having adenomatous polyps, endometrial cancer, stomach or bladder cancer in the family also increases the risk. Although cancers that occur in several generations in the family are caused by environmental or lifestyle factors in many cases, some individuals have a hereditary genetic predisposition. The most common genetic causes of colon cancer are "non-polyposis hereditary colorectal cancer" (HNPCC) and "familial adenomatous polyposis" (FAP).
The risk of cancer recurrence or a second primary cancer in a person who has previously had colon cancer. is higher. The more polyps a person has, the greater the risk of developing cancer. People with chronic inflammatory bowel disease such as ulcerative colitis or Crohn's disease have a higher risk of colon cancer. A diagnosis of type 2 diabetes increases the risk of colon cancer or polyps by 50%. Lifestyle factors that affect type 2 diabetes, such as inactivity, high-calorie diet, and being overweight or obese, also increase the risk. Excessive alcohol consumption, a diet rich in fat, especially red or processed meat, refined grains or animal-derived fats, increase the risk of colon cancer. It is also known that smoking increases the risk.
How Does Colon Cancer Start?
Colon cancers usually begin with benign polyps that appear in the mucosa, the innermost layer of the intestine. Some people are more prone to developing polyps, especially those with a personal or family history of colon cancer, those who carry certain genes linked to colon cancer, and those with type 2 diabetes. Most of these polyps remain benign. However, adenomatous polyps (or adenomas) have a high potential to develop abnormal cells, become precancerous, and eventually turn into cancer.
Adenomas usually grow on a stalk, but they can also be flat. Their development often spans a decade or more. The risk of turning into cancer increases with their growth and development in the colon. It increases with the length of time they spend sleeping. When an adenoma turns into cancer, it is called adenocarcinoma. In its early stages, abnormal cells are inside the polyp. If they are removed at this stage, they may not develop into invasive cancer. On the other hand, as cancer cells multiply within the polyp, they can move to the colon wall or further areas. In advanced cases, tumors have involved all tissue layers of the colon wall. Advanced cancer can also metastasize, reaching cells in the circulatory system and spreading to other organs such as the liver.
Polyps and Cancer
Less than 10% of all adenomas become cancerous. However, 95% of colon cancers develop from adenomas. Some polyps can be removed easily and painlessly during colonoscopy. While large polyps can be caught and cut with the help of a wire lasso passed through a tool called a scope, very small polyps can be removed by applying small electrical currents. Very large polyps may require surgery.
Other cancers, although much rarer, may also occur in the colon. Lymphoma, gastrointestinal stromal tumors and carcinoid tumors are rare colon tumors.
What are the symptoms of colon cancer?
Colon cancer usually does not cause symptoms in the early stages. Many symptoms can be attributed to other digestive diseases. If these symptoms are due to cancer, the disease will progress past its early stages. Therefore, the relevant physician should be consulted in case of signs and symptoms related to digestive problems lasting more than a few weeks.
Possible symptoms of colon cancer:
- Usually going to the toilet. Changes in habits or appearance of stool that last for more than 10 days, such as thin stools, constipation or diarrhoea.
- Bright red blood in the stool or black, tarry stools
- Persistent pain and tenderness in the lower abdomen.
- Bloating, cramping or gas pain.
- Feeling that the rectum is not fully emptied after going to the toilet
- Loss of appetite and weight
- Symptom of blood loss anemia
- Vomiting
- Symptoms of anemia such as fatigue, paleness and heart palpitations
- Not being able to go to the toilet for more than a week, bowel movements It may be a sign of obstruction.
Is it possible to make an early diagnosis?
The development of colon cancer is generally slow, taking 5-10 years. If benign polyps or polyps that have not yet turned into cancer are removed during colonoscopy screenings, colon cancer may be prevented from the very beginning. The type of cancer screening test and how often it is done depends on individual risk status. It is determined by taking into account the person's age, health, cancer history and family cancer history. An annual physical examination and risk assessment are performed for the screening of a 50-year-old individual who has no complaints and has an average risk of colon cancer. If no abnormal findings are detected in these examinations, a fecal occult blood test can be performed once a year, and in addition to this test, a flexible sigmoidoscopy or virtual colonoscopy (CT colonography) can be performed every five years or a colonoscopy every 10 years. During the annual follow-up examination, it is checked whether there are symptoms that may be associated with colon cancer, such as anemia or problems with the digestive system, a rectal examination is performed, fecal occult blood test, fecal immunochemical test or fecal DNA test may be performed.
Stool DNA test may be performed. blood tests; The stool is checked for blood contamination. In polyps and tumors, blood vessels are more delicate, and the passage of stool may cause small amounts of bleeding. Tests that detect human hemoglobin antibodies instead of blood in stool have also been developed. A negative test result does not completely rule out the possibility of colon cancer because some polyps do not bleed. On the other hand, a positive result does not necessarily indicate cancer. Peptic ulcer, inflammatory bowel disease, or irritation due to aspirin and nonsteroidal anti-inflammatory drug (NSAID) use may also cause bleeding in the intestine.
Fecal occult blood test; It is examined in three consecutive stool samples and reveals approximately 50% of colon cancers. To avoid false positive results, some medications are restricted 10 days in advance and some foods are restricted six days in advance. Starting seven days before the test, NSAID group drugs and aspirin are discontinued until the test is completed. Starting three days before the test and during the test, red meat and some fish (containing the animal blood protein hemoglobin) are not consumed, resulting in a false positive result. Citrus fruits, citrus juices, most raw vegetables, more than 250 mg of vitamin C per day, and iron supplements, which can cause erectile dysfunction, are stopped.
The disadvantages of fecal occult blood tests are that they can only detect half of the cancers. It cannot detect non-bleeding polyps and tumors. On the other hand, the rate of false positive results is also high. When positivity is detected, a colonoscopy is required.
Flexible (Fiberoptic) Sigmoidoscopy; shows approximately the last 1/3 of the colon. 60% of colon polyps and cancers originate from the lower part of the colon, and all polyps and tumors originating from there can be detected in sigmoidoscopy. If a pathology such as adenoma is detected, a colonoscopy is required.
Colonoscopy; With colonoscopy, the entire colon, which is approximately 1.5-1.8 m long, is scanned and 95% of colon cancers can be detected. Precancerous polyps can be removed before they turn into cancer. Before the colonoscopy procedure, colon cleansing is required, and bowel evacuation preparations are made with laxatives the day before. Colonoscopy is performed under sedation because it is a painful procedure, this is not general anesthesia. Drugs that have a sedative effect relax the person, relax them, prevent them from feeling pain, and prevent them from remembering that moment with their short-acting forgetfulness effect. The average processing time is 30-60 minutes. The risk of bowel perforation in polyp removal varies between 0.5% and 1% depending on factors such as the size of the polyp, its broad base, and its number. In these cases, surgical repair may be required.
Virtual Colonoscopy (CT Colonography); Computed tomography is used to take three-dimensional images of the colon. Colon cleaning, such as a colonoscopy, is required. Images are taken from outside the body. A tube is inserted into the fecal sac from the anus, air is pumped to inflate the colon, and images are taken with a tomography. It does not require sedative medication. Disadvantages: Radiation is given, it may not detect sessile-flat polyp-lesions, and when a polyp is detected, colonoscopy is required to remove it.
How is the diagnosis made?
Anemia in complete blood count. ) detection may be a sign of cancer. Anemia occurs in bleeding polyps or cancer. If cancer is suspected based on symptoms or findings in patients or laboratory test results, colonoscopy is performed.
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