Understanding Colorectal Cancer

Colorectal Cancer Stages and Classification

This is the seventh page in the Understanding Colorectal Cancer Guide. This guide was developed by the HealthTree Education Team and was last updated and reviewed on April 6th, 2026.

Doctors use "stages" to describe how far cancer has grown and whether it has spread. Knowing the stage of your cancer helps your care team plan the best treatment and understand your prognosis.

For colorectal cancer, the stage is determined based on:

• How far the tumor has grown through the wall of the colon or rectum (T)
• Whether the cancer has spread to nearby lymph nodes (N)
• Whether the cancer has spread to distant organs such as the liver or lungs, called metastasis (M)

Knowing the stage of your cancer will help your care team plan your treatment and understand your prognosis. 

The TNM Staging System

Most colorectal cancers are staged using the TNM system developed by the American Joint Committee on Cancer (AJCC). Your pathology report after surgery will include a detailed TNM designation. Each letter is assigned a number that describes how far the cancer has progressed in that category:

• T (Tumor) describes how far the tumor has grown through the layers of the colon or rectal wall, scored T1–T4.
• N (Nodes) describes whether cancer has reached nearby lymph nodes, scored N0 (none) to N2 (four or more lymph nodes).
• M (Metastasis) describes whether the cancer has spread to distant organs, scored M0 (no spread) or M1 (spread detected).

Colorectal Cancer Stage Groups

Often, TNM staging can be simplified into stages (0-IV). The larger the number, the more advanced the cancer. 

Stage 0 — Carcinoma in Situ ("In Its Original Place")

Abnormal cells are found only in the innermost lining of the colon or rectum (the mucosa). The cells have not grown into deeper layers of the bowel wall.

TNM example: Tis, N0, M0. "Tis" stands for "in situ," meaning the abnormal cells are contained entirely within the inner lining and have not invaded deeper tissue. No lymph nodes are involved (N0) and there is no distant spread (M0).

Stage I

The cancer has grown through the innermost lining into deeper layers of the colon or rectum wall, but has not spread to nearby lymph nodes or distant organs.

TNM example: T1 or T2, N0, M0. The tumor has grown into the inner muscle layers of the bowel wall (T1 = inner layer, T2 = outer muscle layer), but lymph nodes are clear (N0) and there is no distant spread (M0).

Stage II

The cancer has grown through the wall of the colon or rectum and may have reached nearby tissues, but has not spread to lymph nodes. Stage II is divided into IIA, IIB, and IIC based on how far the tumor has grown.

TNM examples:

• Stage IIA: T3, N0, M0. The tumor has grown through the muscle wall into the outermost layer of the colon (T3), but has not broken through into surrounding tissue. No lymph node involvement (N0), no distant spread (M0).
• Stage IIB: T4a, N0, M0. The tumor has grown through the outermost layer of the colon into the lining of the abdominal cavity (T4a). No lymph nodes (N0), no distant spread (M0).
• Stage IIC: T4b, N0, M0. The tumor has grown into or attached to nearby organs or structures (T4b). No lymph nodes (N0), no distant spread (M0).

Stage III

The cancer has spread to nearby lymph nodes but not to distant organs. Stage III is divided into IIIA, IIIB, and IIIC based on the size and location of the tumor and the number of lymph nodes involved.

TNM examples:

• Stage IIIA: T1–T2, N1, M0. A smaller tumor (T1 or T2) that has spread to 1–3 nearby lymph nodes (N1), but no distant spread (M0).
• Stage IIIB: T3–T4a, N1, M0 or T2–T3, N2, M0. A more locally advanced tumor that has spread to nearby lymph nodes, but no distant spread (M0).
• Stage IIIC: T4b, N1–N2, M0. The tumor has grown into nearby organs and spread to lymph nodes (N1 or N2), but no distant spread (M0).

Stage IV (Metastatic Colorectal Cancer)

The cancer has spread to distant organs, most commonly the liver and lungs, but sometimes the peritoneum (the lining of the abdominal cavity), the ovaries, or other organs. Stage IV is divided into IVA, IVB, and IVC based on where the cancer has spread.

TNM examples:

• Stage IVA: Any T, Any N, M1a. The cancer has spread to one distant organ or set of distant lymph nodes (M1a), such as the liver only.
• Stage IVB: Any T, Any N, M1b. The cancer has spread to two or more distant organs (M1b), such as the liver and lungs.
• Stage IVC: Any T, Any N, M1c. The cancer has spread to the peritoneum (M1c), with or without spread to other organs.

Recurrent Colorectal Cancer

Recurrent colorectal cancer is cancer that has come back after treatment. It may return in the colon or rectum (local recurrence) or in distant organs (distant recurrence).