Colorectal cancer is the second deadliest cancer in the United States. Many cases start with a small growth—called a polyp—in the lining of the intestine. Most polyps are harmless, but some may undergo changes over time and develop into cancer.
“The good news is that polyps can be removed before they ever become cancerous,” says Haddon Pantel, MD, a Yale Medicine colorectal surgeon. Cancerous Polyps In Bowel
A routine colonoscopy, the “gold standard” screening test for colorectal cancer, identifies polyps so your doctor can remove them during the same procedure. The polyps are then sent to a pathologist, who will study them under a microscope and assess them for characteristics associated with precancerous changes.
We asked Dr. Pantel three questions about colorectal polyps. His answers are below.
Colon polyps are tissue growths found on the inner lining of the colon or rectum. They vary in shape and size, ranging from less than a quarter-inch in diameter to several inches. As many as 15% to 40% of adults may have polyps. They are more common as people age.
There are two kinds of polyps: Non-neoplastic (or hyperplastic) polyps are small and will never become cancerous. Neoplastic polyps, on the other hand, are precancerous. Adenomas or sessile serrated polyps are neoplastic and can become cancerous if given enough time to grow. (More on this below.)
Cancer develops when cells divide quickly, creating an environment where mutations can occur. “As the cells keep turning over [the process through which cells die and are replaced by new ones], an error can be made in a cell’s DNA. Then, that cell with an error can continue to divide, and there can be a second error,” Dr. Pantel says. Over time, those errors accumulate, and that's what leads to cancer, he adds.
“The lining of the intestine is an area with a lot of cell turnover. That's one of the reasons why the colon is an area where many cancers are formed,” Dr. Pantel says.
Not all colorectal polyps are precancerous, but many have that potential. An estimated 5% to 10% of adenomas may eventually progress to become a cancer.
When a person is found to have multiple or large polyps (which are made of larger masses of cells), there is more opportunity for cancer to develop, Dr. Pantel adds. “A large polyp has been around longer, so it has had more time to undergo those cellular changes.”
Most of these polyps develop sporadically, meaning they appear as people age. But there are hereditary components to some cancers, and people with a family history of colon cancer or polyps are more likely to develop them. “There are syndromes where you have certain mutations you're already born with, so you're predisposed,” says Dr. Pantel. One of these is Lynch syndrome, an inherited cancer syndrome that is the most common cause of inherited colorectal cancer.
First, those polyps will be removed. So, if they are precancerous, that cancer will never develop.
A colonoscopy, which is usually done under sedation, involves the insertion of a long, flexible tube through the anus and into the rectum and colon. It’s the only screening test that allows for the removal of polyps identified during the procedure.
Your doctor can use instruments inserted through a colonoscope to remove and biopsy polyps. “There are also other techniques, including more advanced ones, for taking out large polyps,” Dr. Pantel says.
Polyps are then sent to a pathologist, who will determine whether or not they are precancerous. This is done by thinly slicing polyp tissue, staining it to make it easier to see, and then looking through a microscope for certain features that are characteristic of cancer.
Other tests for colon cancer are less invasive, including virtual colonoscopy, which uses a CT scanner to produce pictures of the colon from outside the body. Or, there are at-home tests, including fecal immunochemical test (FIT), which can detect blood in the stool, and Cologuard®, which can detect both blood and DNA changes. The latter two tests involve sending stool samples to a laboratory for analysis. But if any of these tests suggests a possible cancer, a follow-up colonoscopy will likely be recommended.
As mentioned above, there are several different types of polyps. Neoplastic polyps look different from other polyps. Adenomas may look tubular (like tiny test tubes), villous (with a leaf-like growth pattern), or tubulovillous (a combination of the two). Flattened, broad-based, firmly attached polyps are described as sessile, while those with a saw-tooth appearance are called serrated. All of these polyps are considered precancerous; removing them prevents them from developing into cancer.
Colonoscopy results are usually available within five to seven business days—even quicker if the polyp is small, Dr. Pantel explains. “At that point, you should listen to the advice of your surgeon or gastroenterologist, which will usually include recommendations for continued surveillance,” he says.
The U.S. Preventive Services Task Force recommends adults ages 45 to 75 be screened every 10 years (sometimes more if they have an increased risk). “If cancer is not found, but there were multiple polyps and/or large polyps, you may have to return sooner—maybe in five years, three years, or even in one,” Dr. Pantel says. “It just depends on the number and the size of the polyps.” Some people who are at increased risk for colon cancer, including some Millennials and Gen Zers, may need to be screened earlier than age 45 and/or more frequently.
Polyps don’t usually cause symptoms, so anyone can have potentially cancerous polyps and not know it. That’s why it’s important to talk to a medical professional if you notice any of the following symptoms of colon cancer: a change in bowel habits; blood in your stool; diarrhea, constipation, or feeling that the bowel does not empty all the way; abdominal pain, aches, or cramps that don’t go away; or unexplained weight loss.
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