The staging system most often used for colorectal cancer is the American Joint Committee on Cancer (AJCC) TNM system, which is based on 3 key pieces of information:

• The extent (size) of the tumor (T): How far has the cancer grown into the wall of the colon or rectum? These layers, from the inner to the outer, include:
  • The inner lining (mucosa), which is the layer in which nearly all colorectal cancers start. This includes a thin muscle layer (muscularis mucosa).
  • The fibrous tissue beneath this muscle layer (submucosa)
  • A thick muscle layer (muscularis propria)
  • The thin, outermost layers of connective tissue (subserosa and serosa) that cover most of the colon but not the rectum
  • The spread to nearby lymph nodes (N): Has the cancer spread to nearby lymph nodes?
  • The spread (metastasis) to distant sites (M): Has the cancer spread to distant lymph nodes or distant organs such as the liver or lungs?The system described below is the most recent AJCC system effective January 2018. It uses the pathologic stage (also called the surgical stage) which is determined by examining tissue removed during an operation. This is also known as surgical staging. This is likely to be more accurate than clinical staging, which takes into account the results of a physical exam, biopsies, and imaging tests, done before surgery.

    Numbers or letters after T, N, and M provide more details about each of these factors. Higher numbers mean the cancer is more advanced.”

American Cancer Society (https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/staged.html)