Dr. Roberts Offers an Explanation of Colorectal Cancer Screening
This week I want to talk about screening for colorectal cancer (CRC). Fortunately, screening for this type of cancer has become more common due to increased public awareness aided by campaigns such as CDC’s Screen for Life Action Campaign cdc.gov/cancer/colorectal/sfl/.
There were approximately 148,000 cases of CRC in 2020 and 53,000 deaths, making it the fourth deadliest cancer in men and third deadliest in women. If caught when the disease is localized to the colon, 90 percent of patients live at least five years after diagnosis. However, only 39 percent of people are diagnosed in early stages.
The good news is that the number of new cases and deaths has continued to drop over the last decade or so. The decreases are likely due to more people undergoing recommended screening, but may also be due to other factors as well. However, we are seeing a worrying trend of it appearing at younger ages. Actor Chadwick Boseman died at age 42.
Colorectal cancer warning signs include blood in the stool, persistent abdominal pain, change in bowel movements (especially smaller diameter stools), unexplained weight loss, and iron-deficiency anemia.
An advertisement that ran in the New York Times a few years ago listed three early warning signs of colon cancer: You feel great; You have a healthy appetite; You’re only 50. This was a brilliant piece, educating people that they can have CRC without any warning signs.
The risk of developing CRC increases with age (93 percent of cancers occur after age 50). A family history of a sibling or parent with CRC or colon polyps also increases the risk for CRC, though 75 percent of CRC occurs in patients with no family history.
Inflammatory bowel disease (Crohn’s disease & ulcerative colitis) also increase the risk of CRC. Not exercising regularly, eating a diet high in fat and low in fruits, vegetables and fiber, cigarette smoking, being obese, or drinking too much alcohol are also risk factors.
Colorectal cancer usually begins as a small nest of abnormal mucus-secreting gland cells in the wall of the colon (large intestine). The cells eventually grow into finger-like projections inside the colon called polyps. These polyps are not cancerous, but they have the potential to develop into cancer. There are two types of polyps, adenomatous and hyperplastic. Adenomatous polyps may become cancerous, while the hyperplastic variety do not.
The goal of any cancer screening program is to either find abnormal appearing cells before they have turned into cancer or discover a cancer when it is very small. There are a number of different methods to screen for CRC. Different professional groups have produced various screening recommendations. Descriptions of the various screening methods can be found in the reference link at the end of this article.
CRC screening tests that can detect adenomatous polyps and cancer includes flexible sigmoidoscopy (a scope that visualizes the lower part of the colon), colonoscopy (a scope that looks at the entire colon), double-contrast barium enema (an X-ray procedure where dye and air are pumped into the colon), and “virtual colonoscopy” (an X-ray study using a CT scan to construct a three dimensional image of the colon). Flexible sigmoidoscopy and colonoscopy offer the added benefit of allowing the physician to biopsy and remove polyps or suspicious lesions at the time of screening.
Colonoscopy is certainly the gold standard for detection of CRC, but many patients are sometimes squeamish about having one. There are other less invasive tests that can be done, though they are not as sensitive at detecting polyps and cancer.
Less invasive tests include high-sensitivity fecal occult blood testing (FOBT) and fecal immunochemical testing (FIT). FOBT is falling out of favor as it involves following a specific diet and submitting multiple stool samples to a doctor or lab where they are tested for microscopic blood.
The FIT test has, for the most part, supplanted the FOBT in most doctors’ offices. It has the advantage of not requiring dietary restrictions prior to doing the test and can be performed on a single stool specimen. It is also specific for human blood proteins whereas the FOBT may detect animal blood protein that a patient consumed, yielding a false positive test. If any of these tests are positive, usually patients should have a colonoscopy to locate the source of the bleeding.
The newest test to gain FDA approval is Cologuard®, a stool test that uses a combination of FIT and a test for DNA specific to colon cancer cells. This test has some potential problems including a high false positive rate of 13 percent (the test is positive, but the patient does not have cancer). The FIT test has about a five percent false positive rate.
If you are over 45 or have other risk factors, you should speak to your doctor about what test or combination of tests may be right for you. The United States Preventive Services Task Force gives its highest “Grade A” recommendation for screening patients ages 50 to 75, and “Grade B” recommendation for starting screening at age 45. Screening for those over 75 is generally not recommended unless a physician feels there are other circumstances that warrant it.
Since the Affordable Care Act was signed into law, all insurance companies are required to pay for recommended screening for CRC with no patient cost sharing such as co-pays or deductibles. However, if a patient has a colonoscopy or sigmoidoscopy and a polyp is found, the patient will likely incur the cost of the biopsy procedure and pathology charges to examine the tissue.
For more detailed information, you can visit bit.ly/1znlju6 for the latest Colorectal Cancer Facts & Figures.
Dr. John Roberts is a retired member of the Franciscan Physician Network specializing in Family Medicine.