Understanding the purpose of colorectal cancer screenings
A colon cancer screening, also called colorectal screening, is a test that looks for early signs of colon cancer before symptoms appear. Most colon cancers start as polyps, which are noncancerous masses that grow on the inner walls of the colon. Polyps tend to grow slowly. A small percentage of these growths turn into cancer. It usually takes a long time (around 10 years) for a polyp to turn into cancer. Colon cancer screening can detect colon cancer and polyps early, which gives you the best chance at successful treatment.
Colon cancer screening guidelines
Medical experts recommend people at average risk of colon cancer start getting screened at age 45. If colon cancer runs in your family, your doctor may recommend screening earlier or more often.
You may need to be tested earlier or more frequently if you have:
- Inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
- A personal or family history of colon cancer or colorectal polyps
- Genetic factors like Lynch syndrome, familial adenomatous polyposis (FAP), or hereditary non-polyposis colorectal cancer
Colon cancer screening tests
Colorectal screening tests help your doctor find cancer early, when it’s easier to treat and before symptoms show up. While diagnostic tests are used when a patient is showing symptoms and needs a diagnosis, screening tests are intended for healthy patients without symptoms.
A colonoscopy is the most comprehensive test for colon cancer screening. It takes about 30 to 60 minutes. It’s usually repeated every 10 years if no abnormalities are found, and you don’t have an increased risk of colon cancer. Abnormal polyps are removed during the exam. The procedure is done in an outpatient hospital setting and requires preparation.
To prepare for your colonoscopy:
- Don’t eat solid food the day before the test.
- Adjust any medications you’re taking, if necessary.
- Completely empty your intestines and bowels before the test.
Before your screening, your provider will give you detailed instructions for how and when to begin your colonoscopy preparation.
What happens during a colonoscopy?
During a colonoscopy, you’ll receive anesthesia to keep you relaxed and pain-free. While you lie on a table, the doctor will insert a small camera (colonoscope) through your anus into your rectum and colon. The camera allows the doctor to examine your large intestine for abnormalities like polyps and to take tissue samples if needed.
Polyps are common and usually harmless, but because colon cancer often starts as a polyp, your doctor may remove them to prevent cancer.
After the procedure, you will be monitored in a recovery area as you wake up from anesthesia. You might feel some cramping or bloating for a few hours.
Virtual colonoscopy (CT colonography)
Your care team will provide aftercare instructions. You won’t be able to drive, so plan for a friend or family member to take you home. Most people can return to normal activities the next day.
A virtual colonoscopy uses a CT scan to create cross-section images of the abdominal organs, helping to find changes or abnormalities in the colon. It takes about 10 minutes and is typically performed every five years.
This procedure doesn’t need sedation or a scope inside the colon. However, it does require complete bowel cleaning, as well as diet and medication adjustments beforehand. Since tissue samples cannot be taken during a virtual colonoscopy, a follow-up colonoscopy may be needed.
Stool DNA tests, like Cologuard, use a stool sample to look for DNA changes that might indicate colon cancer or precancerous conditions. You collect a stool sample at home and send it to a lab for testing. This test is usually done every three years.
However, this test is less sensitive than a colonoscopy at detecting precancerous polyps, so if abnormalities are found, additional tests may be needed.
Fecal occult blood test and fecal immunochemical test are lab tests that look for hidden (occult) blood in your stool and are repeated every year.
These tests may not detect some polyps and cancers. Before the tests, certain foods and medications might need to be avoided for several days. If occult blood is detected, further tests may be needed.
High-sensitivity guaiac fecal occult blood test uses a chemical substance called guaiac to check for blood in three consecutive stool samples. The small samples of stool, which are collected at home, are placed on a special card and returned to a doctor or laboratory for testing. If used, this test is recommended to be done annually.
Flexible sigmoidoscopy is an exam that’s used to evaluate the lower part of the colon using a flexible tube with a tiny video camera at the tip. If necessary, the doctor may also perform a biopsy during this procedure. This exam is recommended every five years.
Screening for hereditary colon cancer
Some colon cancers are caused by gene mutations that can be passed down in families. If colon cancer runs in your family, your doctor may recommend earlier or more frequent screening tests.
The most common genetic syndromes linked to colon cancer are Lynch syndrome and familial adenomatous polyposis.
We offer in-depth expertise in colon cancer genetics. Penn Medicine’s Gastrointestinal Cancer Genetics Program provides screening services to help you understand your risk for hereditary colon cancer, so you can make informed decisions about your health.
Rated “exceptional” by The National Cancer Institute
Penn Medicine’s Abramson Cancer Center is a world leader in cancer research, patient care, and education. Our status as a national leader in cancer care is reflected in our continuous designation as a Comprehensive Cancer Center by the National Cancer Institute (NCI) since 1973, one of 7 such centers in the United States. The ACC is also a member of the National Comprehensive Cancer Network, one of a select few cancer centers in the U.S., that are working to promote equitable access to high-quality, advanced cancer care.