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.
Colorectal cancer can occur without polyps, but it is thought to be an uncommon event. Individuals with long-standing inflammatory bowel diseases, such as chronic ulcerative colitis and Crohn's colitis, are at increased risk for developing colorectal cancer that occurs in the absence of obvious polyps.
Bowel cancer risk
Doctors believe that most bowel cancers develop from adenoma polyps. But very few polyps will turn into cancer, and it takes many years for this to happen.
Almost all colon cancers start in the lining of the colon and rectum. When doctors talk about colorectal cancer, this is usually what they are talking about. There is no single cause of colon cancer. Nearly all colon cancers begin as noncancerous (benign) polyps, which slowly develop into cancer.
How long does it take for a polyp to turn into cancer? The growth and mutation of colon polyps into cancer is a slow process, taking an estimated 10 years on average. So as long as patients are screened, it is unlikely they will develop cancerous polyps.
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.
It takes approximately 10 years for a small polyp to develop into cancer.
Diarrhea, constipation, or feeling that the bowel does not empty completely. General abdominal discomfort, such as frequent gas pains, bloating, fullness and/or cramps. Constant feeling of fatigue or tiredness.
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.
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.
Giant lipomas (>4 cm) are the most common benign tumors in the colon that cause intussusception, although no specific incidence data have been documented. Even patients with large lipomas may have nonspecific or intermittent symptoms, which causes delay and difficulty in making the diagnosis.
Polyps are common in American adults, and while many colon polyps are harmless, over time, some polyps could develop into colon cancer. While the majority of colon cancers start as polyps, only 5-10% of all polyps will become cancerous. The size of a polyp typically does make a difference.
In 1 to 7 years, depending on a variety of factors: The number, size and type of polyps removed; if you have a history of polyps in previous colonoscopy procedures; if you have certain genetic syndromes; or if you have a family history of colon cancer.
Colorectal cancers can often bleed into the digestive tract. Sometimes the blood can be seen in the stool or make it look darker, but often the stool looks normal.
Because early stages of colon cancer can go unnoticed for years, screening is important for early detection. It is generally recommended that individuals at average risk for colon cancer receive a screening test every 10 years.
Signs and symptoms of colon cancer include: A persistent change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool. Rectal bleeding or blood in your stool. Persistent abdominal discomfort, such as cramps, gas or pain.
intermittent, and occasionally severe, abdominal pain – this is always brought on by eating. unintentional weight loss – with persistent abdominal pain. constant swelling of the tummy – with abdominal pain. being sick – with constant abdominal swelling.
Some cancers (such as colon cancer) present with a dull ache in the lower belly, or lower back. For some, this may feel less like an obvious pain, and more like a discomfort. Bellyaches that persist should not be ignored, as they can be a warning sign of a more serious problem.
In most cases, colon and rectal cancers grow slowly over many years. Most of those cancers start as a growth called a polyp. Taking out a polyp early may keep it from turning into cancer.
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.
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.
Most polyps grow slowly and take from between 10 and 15 years to become cancerous.
Here's what we know: As often as 40% of the time, a precancerous polyp — frequently a type called an adenoma — is found during a screening colonoscopy. Colon cancer is found during only in about 40 out of 10,000 screening colonoscopies, Dr. Sand said.
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.