It takes approximately 10 years for a small polyp to develop into cancer. Family history and genetics — Polyps and colon cancer tend to run in families, suggesting that genetic factors are important in their development.
Adenomas: Many colon polyps are the precancerous type, called adenomas. It can take seven to 10 or more years for an adenoma to evolve into cancer—if it ever does. Overall, only 5% of adenomas progress to cancer, but your individual risk is hard to predict.
Colon cancer, or cancer that begins in the lower part of the digestive tract, usually forms from a collection of benign (noncancerous) cells called an adenomatous polyp. Most of these polyps will not become malignant (cancerous), but some can slowly turn into cancer over the course of about 10-15 years.
Approximately 6% of colorectal cancers are diagnosed within 3 to 5 years after the patient received a colonoscopy, according to findings from a recent population-based study.
This means cancer and polyps can sometimes go undetected. So, despite having had a 'clear' colonoscopy, some patients go onto develop bowel cancer – referred to as post-colonoscopy colorectal cancer (PCCRC) or 'undetected cancer'.
Colon cancer is typically slow-growing, starting as a benign polyp that eventually becomes malignant. This process may occur over many years without producing any symptoms. Once colon cancer has developed, it may still be years before it is detected.
Usually if a suspected colorectal cancer is found by any screening or diagnostic test, it is biopsied during a colonoscopy. In a biopsy, the doctor removes a small piece of tissue with a special instrument passed through the scope. Less often, part of the colon may need to be surgically removed to make the diagnosis.
Screening for colorectal cancer
Colorectal cancer doesn't just appear suddenly. It starts as a small growth on your colon, called a polyp, which rarely causes symptoms. If left alone over many years, polyps can grow into cancer. The only way to know it's there is to look.
In most cases, colon and rectal cancers grow slowly over many years.
In fact, about 90% of people treated for stage 1 colon cancer live at least 5 years after the cancer is found. That being said, colon cancer can come back, which is called recurrence. But the risk of this with stage 1 colon cancer is low compared with other stages.
Some patients under 50 experience symptoms for up to a year before seeing a doctor prompting some experts to encourage earlier screening. Many younger patients with colon cancer are initially misdiagnosed, which often leads to their disease being discovered at an advanced stage.
Colorectal cancer can occur in young adults and teenagers, but the majority of colorectal cancers occur in people older than 50. For colon cancer, the average age at the time of diagnosis for men is 68 and for women is 72. For rectal cancer, it is age 63 for both men and women.
In general, colorectal cancers tend to be slow growing, gradually enlarging and eventually penetrating the bowel wall. When they do spread, it is usually through invasion of nearby lymph nodes. In fact, cancer cells may enter a lymph node even before the tumor penetrates through the intestinal wall.
Most polyps are benign (not cancerous). Your doctor can tell if a colon polyp is cancerous during a colonoscopy by collecting tissue to biopsy. The results of the biopsy are typically sent to your doctor within a week. Only 5% to 10% of all polyps become cancerous.
If the cancer has not spread and is localized to the colon, then the 5-year survival rate is 91%. However, if the cancer has spread to the nearby tissues or lymph nodes, the 5-year survival rate is 72%. The survival rate drops to 14% if the cancer spreads to distant parts of the body.
Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps. Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp turning into cancer depends on the type of polyp it is.
Colon cancer most often spreads to the liver, but it can also spread to other places like the lungs, brain, peritoneum (the lining of the abdominal cavity), or to distant lymph nodes. In most cases surgery is unlikely to cure these cancers.
Many cases of colon cancer have no symptoms. If there are symptoms, the following may indicate colon cancer: Abdominal pain and tenderness in the lower abdomen.
Early symptoms of colon cancer might include blood in the stool; persistent problems in defecating (long-lasting diarrhea or constipation); feelings of cramping, distension or pain in the area of the bowel; or a persistent decrease in the size of the stool.
Colon cancer is considered a silent disease. Most of the time there are no symptoms. The symptoms that people may experience include a change in bowel habits, abdominal pain, blood in the stool, and weight loss. If individuals have these symptoms, the disease may already have advanced.
After a colonoscopy, eat foods that are soft and easy to digest to ease side effects such as bloating or gas. This may include eggs, white toast, and applesauce for breakfast. For lunch or dinner, choices could include lean chicken without skin, mashed potatoes, and soft-cooked carrots.
A colon polyp is a small clump of cells that forms on the lining of the colon. Most colon polyps are harmless. But over time, some colon polyps can develop into colon cancer, which may be fatal when found in its later stages.
If you've been diagnosed with colon cancer, your doctor may recommend tests to determine the extent (stage) of your cancer. Staging helps determine what treatments are most appropriate for you. Staging tests may include imaging procedures such as abdominal, pelvic and chest CT scans.