Colorectal Cancer Stages: From 0 to IV

This page is for people with colorectal cancer, and their families, who want to understand what each stage means. It walks through stages 0 to IV and explains why stage is not the whole story.

Staging describes how far colorectal cancer has grown and spread. Doctors use the AJCC TNM system, now in its 8th edition, effective since 2018. TNM stands for three things checked together: how deep the tumor (T) has grown into the bowel wall, whether it has reached nearby lymph nodes (N), and whether it has spread to distant organs (M). These three pieces combine into an overall stage from 0 to IV.

Staging usually combines findings from surgery, imaging scans, and the pathology report on tissue removed during surgery or biopsy. The final stage may not be confirmed until after surgery, once the removed tissue has been fully examined.

Stage 0 means the abnormal cells are still confined to the innermost lining of the colon or rectum. They have not grown into deeper layers. This is sometimes called carcinoma in situ. It is usually found and removed during a colonoscopy, often before it would ever be called invasive cancer.

In stage I, cancer has grown through the inner lining into deeper layers of the bowel wall. It has not reached the lymph nodes or spread elsewhere. Surgery alone often cures stage I colorectal cancer.

Stage II means cancer has grown through the full thickness of the colon or rectal wall, or into nearby tissue. It still has not reached the lymph nodes or distant organs. Doctors divide this into IIA, IIB, and IIC. The letters depend on exactly how far the tumor has grown. They also depend on whether it has reached nearby organs or the lining of the abdomen. Despite growing further, stage II cancer is still local. Surgery is central, and chemotherapy is added only for some higher-risk cases.

In stage III, cancer has spread to nearby lymph nodes, whether or not it has grown through the bowel wall. The subgroups IIIA, IIIB, and IIIC describe two things: how many lymph nodes are involved, and how deep the tumor has grown. More lymph nodes involved generally means a higher substage. Once cancer reaches the lymph nodes, chemotherapy after surgery becomes standard treatment, not just an option considered for high-risk cases.

Stage IV means the cancer has spread beyond the colon or rectum and its nearby lymph nodes, to organs like the liver or lungs, or to distant lymph nodes or the lining of the abdomen. Doctors divide this into IVA, IVB, and IVC. This depends on how many distant sites are involved. It also depends on whether the abdominal lining is affected. Stage IV colorectal cancer is treated mainly with drugs that reach the whole body, though surgery can still play a role if the spread is limited to a small number of spots.

Two tumors at the same stage can behave differently. Tumor grade, which describes how abnormal the cells look under a microscope, affects how aggressively a cancer tends to grow. Specific genetic features of the tumor matter too. These include microsatellite instability (MSI) and mismatch repair status, which describe how well the tumor's cells fix errors in their DNA. They affect which treatments will work. Your age and overall health matter. So does how your body handles treatment. A stage number alone cannot predict any of that. Stage is a starting point for a treatment plan, not a prediction of what will happen to you specifically.

• What is my exact stage and substage, and what does that mean for treatment?
• Was my stage confirmed by surgery, or is it based on scans so far?
• Does my tumor have features, like MSI-H status (high microsatellite instability, a sign the cell's DNA repair system is not working), that affect my treatment options?
• How will you monitor for recurrence after treatment ends?

• American Cancer Society — Colorectal Cancer Stages
• American Cancer Society — Treatment of Colon Cancer, by Stage