No, although most colon cancers arise from polyps, some do not. Some arise within the wall of the colon. These cancers may be flat or even depressed (excavated). They are more difficult to identify and treat, and they are more likely to spread into the wall of the colon and nearby lymph nodes than cancers originating in polyps. This is particularly true of serrated adenomatous polyps which usually are flat rather than polypoid in appearance.There also is a familial, genetic syndrome called hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) in which colon cancers occur with very high incidence (80% or more of patients). There are few or no polyps to identify in these patients. Moreover, the cancers occur at a younger age, often prior to the time screening for colon cancer is recommended to begin, and the syndrome is not recognized until a family member develops cancer usually at a young age. HNPCC is suspected because other family members also have colon cancer and certain criteria are met (Amsterdam or Bethesda criteria), or the cancer shows a particular pattern under the microscope with special stains. If HNPCC is suspected, genetic testing on the cancer can be done to identify the hereditary mutation, and other family members can be tested for the same mutation. If present, the family members can undergo a screening colonoscopy and follow-up surveillance colonoscopies. HNPCC may be associated with cancers in tissues outside the colon as well. Fortunately, HNPCC is responsible for only a few percent of all colon cancers.