We're lucky to have such a good screening test for colon cancer - colonoscopy can not only detect tumors while they're curable, but it can identify precancerous polyps which can be removed before they become cancerous.
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.
As patients, we assume that a colonoscopy will always detect any cancer and any polyps. However, in reality, things are just not that simple. Tumours and polyps can look different in each patient and at different stages of their growth or be obscured from the view of the camera.
Completely preventable cancer
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.
Colonoscopies can detect conditions like colitis, inflammatory bowel disease and diverticulosis. But mainly, doctors are looking for precancerous or cancerous colon polyps, which are growths on the inside of the colon's lining.
If your doctor thinks an area needs further evaluation, he or she might pass an instrument through the colonoscope to obtain a biopsy (a small sample of the colon lining) to be analyzed. Biopsies are used to identify many conditions, and your doctor will often take a biopsy even if he or she doesn't suspect 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.
The 3 main symptoms of bowel cancer are blood in the stools (faeces), changes in bowel habit – such as more frequent, looser stools – and abdominal (tummy) pain. However, these symptoms are very common and most people with them do not have bowel cancer.
Colonoscopy Isn't Perfect: About 6% of Colorectal Cancers Are Missed | University of Utah Health.
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.
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.
There's no debate that colonoscopy is still the most effective screening exam for colon cancer. The first-rate exam not only detects colon cancers with about 98% accuracy, but it also allows doctors to remove precancerous and cancerous polyps during the procedure.
If you're wondering how long you can have cancer without knowing it, there's no straight answer. Some cancers can be present for months or years before they're detected. Some commonly undetected cancers are slow-growing conditions, which gives doctors a better chance at successful treatment.
Results: Among those who underwent colonoscopic screening, 78.9 percent had no detected lesions, 10.0 percent had hyperplastic polyps, 8.7 percent had tubular adenomas, and 3.5 percent had advanced neoplasms, none of which were cancerous (95 percent confidence interval for cancer, 0 to 0.4 percent).
However, it will take some time to receive your test results from the lab that will confirm or rule out cancer. Your doctor may have some information for you prior to the lab test results, but the official results will come from the lab within a couple weeks.
If the cancer is diagnosed at a localized stage, the survival rate is 91%. If the cancer has spread to surrounding tissues or organs and/or the regional lymph nodes, the 5-year survival rate is 72%. If colon cancer has spread to distant parts of the body, the 5-year survival rate is 14%.
Colon cancer and polyps: 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.
In most cases, colon and rectal cancers grow slowly over many years.
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.
Surgery is the main treatment. People with very early colon cancer (stage 1) do not usually need chemotherapy. But this might change after surgery. After your operation, a specialist doctor (pathologist) looks closely at your cancer.
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.
Complications related to colonoscopy include, but are not limited to, the following: Continued bleeding after biopsy (tissue sample) or polyp removal. Nausea, vomiting, bloating or rectal irritation caused by the procedure or by the preparatory bowel cleansing.