The most commonly used system for staging colorectal cancer is the TNM system, which is based on tumor size, lymph node involvement, and metastasis. For colorectal cancer, tumor size tends to refer to not only the diameter of the tumor, but if it has grown into the wall of the colon/rectum. Lymph node involvement and metastasis is to measure if the cancer has spread to the nearby lymph nodes or other, more distant parts of the body. By using these three measurements, the American Joint Committee on Cancer (AJCC) classifies colorectal cancers into four stages. [1] 

The first stage is Stage 0, where the cancer is referred to as carcinoma in situ or intramucosal carcinoma. The cancer is at its earliest stage and has not grown beyond the innermost layer (the mucosa) of the colon/rectum. Stage I is when the cancer has expanded beyond the inner layer of the intestine and entered the fibrinous tissue of the submucosa and possible into the muscle layer (muscularis propria). In Stages 0 – I, the cancer has not spread to nearby lymph nodes or distant parts of the body. Stage II is generally classified as being when the cancer has spread to the outermost layers of the colon/rectum, but there is still no lymph node involvement or metastasis observed. Stage III colorectal cancer is generally classified as having colorectal cancer that has lymph node involvement, meaning that the cancer has spread to the nearby lymph nodes, but no metastasis is observed. Stage IV is when metastasis, or the spread of the cancer to distant organs, is observed. Stages II – IV consist of substages based on different aspects such as has far into the colon/rectum wall the cancer has spread, the number of lymph nodes involved, and the extent of metastasis. [1]

Understanding colorectal cancer staging and substages can be a lot to take in, so if you have any questions about your cancer’s exact stage or what the stage means, you should contact your physician and have them to explain your stage in more detail.

References: 

1.     Colorectal cancer stages: Rectal cancer staging: Colon cancer staging. https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/staged.html (accessed Jan 19, 2022).