What is colorectal cancer?

Colorectal cancer includes colon and rectal cancers. Most colorectal cancers start as a growth of polyps on the inner lining of the colon or rectum and can slowly change into cancer over time. Not all polyps become cancer. The chance of a polyp becoming cancerous depends on its type. Two main kinds include:

  • Adenomatous polyps (adenomas) – some of which develop into cancer over a period of ten to fifteen years. 
  • Serrated polyps: there are different types of serrated polyps, some of which are potentially pre-cancerous.

Very few polyps develop into cancer. Therefore, it is very uncommon to find colorectal cancer on a screening exam. Furthermore, by doing a screening test, we can potentially find polyps and remove them before they have a chance to develop into colorectal cancer. In this way, colorectal cancer can actually be prevented.

Colorectal cancer starts in the innermost layer (the mucosa) of the colon or rectum and can grow outward through other layers. It can travel to other parts of the body such as blood vessels, lymph vessels, lymph nodes, or further. The extent of spread outside the walls of the colon and rectum is referred to as staging. Your medical oncologist will discuss the specifics of your stage and treatment options with you.

More information about colorectal cancers (National Cancer Institute)

What colorectal cancer is not

Colorectal cancers are gastrointestinal cancers that begin in the colon (large intestine) or rectum. They should not be confused with other gastrointestinal cancers such as stomach, liver, pancreas, neuroendocrine, anal or GIST because these cancers can have different symptoms, outlooks, and treatments.

Cancers that occur in the colon

  • Adenocarcinomas – the most common type of colorectal cancers, adenocarcinomas start in cells that make mucus to lubricate the inside of the colon and rectum. 
  • Carcinoid tumors – start from cells in the intestine that produce hormones.
  • Squamous cell cancer – the most common type of anal cancer.


For someone who is thought to have colorectal cancer, it's possible that you could have one or more of the following tests (but not all of these will apply to your condition):

  • Imaging (CT scan)
  • Lower endoscopy or colonoscopy
  • Biopsy
  • Physical exam by your medical oncologist
  • Meeting with your surgeon and radiation oncologist


Depending on your unique set of conditions, your treatment could include one or more of the following treatments (but not all of these will apply to your condition):

  • Chemotherapy
  • Radiation
  • Surgery

Your full team of care providers will work closely together to review your diagnostic tests, identify the best course of treatment particular to you, and help you understand your diagnosis and what to expect with any treatment you have.