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While most are harmless, there is a correlation between colon polyp size and cancer risk. Colon polyps that continue growing, or that become very large, may become cancerous, so doctors remove them. Anyone can develop colon polyps, and about 6% of children have them. However, the risk of colon polyps and colon cancer increases with age. About a third of people over 50 have polyps. More than 95% of colon cancer begins with colon polyps. The risk of polyps smaller than 5 millimeters (mm) being cancerous is very low. In larger polyps, the risk of cancer increases. Colon polyps grow very slowly and often do not cause symptoms. Regular colon cancer screenings can help detect them before they become cancerous. Read on to learn more about colon polyp size and cancer risk, including some other potential symptoms of colorectal cancer and treatment options. What are polyps and why might they lead to cancer Share on PinterestThe Good Brigade/Getty ImagesCancer happens when cells grow out of control, creating tumors. Colon cancer is no exception. Colon cancer usually begins with an atypical growth in the colon. Doctors call these growths polyps. Not all polyps are cancerous. However, having a polyp is a risk factor for eventually developing cancer. At least 95% of colon cancers begin with polyps. It can take years for these polyps to develop into cancer. This is why colon cancer screenings are so effective at preventing cancer before it spreads. Doctors divide colon polyps into several subtypes: tubular: a tube-like projectionvillous: a finger-like projection Both can be cancerous or precancerous, but larger growths are more likely to be villous. An adenoma is a colon polyp that may turn into cancer. There is no set size at which a polyp will become cancerous, nor any particular size that is always cancerous. Even among large polyps, the majority are not cancerous. Polyp size and cancer risk A 2018 study of polyp size and cancer included 550,811 polyps. The majority (81%) were 1–9 mm in diameter. Only a small percentage of polyps (3.4%) were cancerous. However, cancer rates were highest among the largest polyps. The percentage of polyps that were cancerous, by size, was as follows: Polyp sizePercentage cancerous1–5 mm0.6%6–9 mm2.1%10 mm+13.4% A 2018 study in China correlated polyps larger than 31 mm with a higher risk of colon cancer. People over the age of 50 were more likely to have cancer and polyps, especially large polyps. Another 2018 study supports this finding. The study analyzed a total of 15,906 polyps. Among polyps larger than 30 mm in size, 4.6% were cancerous. Incidence of cancer in polyps less than 5 mm in size was 0%. Other signs and symptoms of colon cancer Colon polyps grow slowly, and people with either polyps or colon cancer may not have any symptoms. This is why colon cancer screenings are so important. People who do have symptoms may experience: rectal bleedingbleeding during a bowel movementfeeling like their bowels are not empty after a bowel movementfrequent constipation or diarrheapain in their stomach changes in bowel habits Treatment A doctor can usually remove colon polyps at the same time as when they detect them. During a polypectomy, a doctor removes the polyp. This allows them to test the polyp for cancer and prevent noncancerous and precancerous polyps from growing and developing into cancer. Depending on the number and size of polyps, a doctor may recommend additional or more frequent colon cancer screenings. If the polyps are cancerous, a doctor may recommend surgical resection. This is the removal of a portion of the colon to prevent cancer from continuing to grow. Most early stage cancers do not require chemotherapy if a doctor is able to remove the cancer. However, more advanced stages may require chemotherapy. Some types of colon cancer respond to targeted immunotherapy drugs. Immunotherapy supports the immune system to recognize and treat cancer. The right treatment depends on:the cancer itselfthe health of the person with cancerhow advanced the cancer iswhether it has spread to other areas of the body The right treatment also depends on the unique features of the cancer, which experts refer to as the histology. Treatment will also depend on whether the cancer has certain mutations. Outlook Early removal of colon polyps has a good outlook. However, people with a history of polyps may develop more polyps. Certain conditions, such as intestinal polyposis, may increase the risk of a person developing more polyps. A person with these conditions has a higher lifetime risk of colon cancer and may need more frequent screenings. Lynch syndrome or familial adenomatous polyposis (FAP) are genetic predispositions that also increase the risk for these cancers. About half of people with colorectal cancer develop cancer that spreads, usually to the liver. Once colorectal cancer spreads, the outlook is less favorable, with most people living only 5 or 6 months. However, in the early stages, if a doctor is able to completely remove the cancer, the outlook is good and it may be possible to cure the cancer. A person may need ongoing cancer screenings for the rest of their life. Summary Many people may avoid or delay having a colonoscopy. However, it remains a highly effective tool for detecting colon polyps and the early stages of colon cancer. These polyps typically grow slowly, allowing plenty of time for detection and removal before they become cancerous. Without screening, they may go undetected, allowing cancer time to grow and spread. It is much easier to treat polyps and early stage cancer than it is to treat advanced colon cancer. People over age 50, as well as people who have a high risk of colon cancer, should discuss a screening test with a doctor. People should also note that there are other colon cancer screening options available. Learn more about colon cancer screening here. Last medically reviewed on May 23, 2022Colorectal CancerCancer / OncologyGastroIntestinal / GastroenterologyMedically reviewed by Faith Selchick, DNP, AOCNP, Nursing, Oncology — By Zawn Villines on May 23, 2022 Latest newsWhat sets 'SuperAgers' apart? Their unusually large neuronsOmega-3 may provide a brain boost for people in midlifeSeasonal affective disorder (SAD): How to beat it this fall and winterCDC: Monkeypox in the US 'unlikely to be eliminated in the near future'Why are more women prone to Alzheimer's? New clues arise Related CoverageWhat to know about colon polypsMedically reviewed by Saurabh Sethi, M.D., MPH Colon polyps are common, especially in those over 50 years of age. 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