Colon & Rectal Cancer Staging

When colon or rectal cancer is found after a biopsy, your doctor will recommend tests to determine if the cancer has spread and, if so, how far. This process, known as staging, helps your care team plan the most effective treatment. 

Tests Used for Staging Colorectal Cancers

Various test results are used to stage colorectal cancer. Many of the tests were run as part of the diagnosis process.

Imaging tests may be repeated to examine other areas of the body for cancer spread, including lymph nodes and nearby organs. Additionally, the oncologist will most likely request biomarker testing of the tumor. Biomarker or molecular testing involves laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the cancer. 

Sometimes, the stage of the cancer cannot be determined until after colon cancer surgery, when lymph nodes are also removed for testing.

Staging of Colorectal Cancer

The TNM system, created by the American Joint Committee on Cancer (AJCC), is the most frequently used staging system for colorectal cancer.

TNM stands for: 

• T: The size and extent of the primary tumor
• N: Whether the cancer has spread to nearby lymph nodes
• M: Whether the cancer has spread (metastasized) to other parts of the body

Doctors assign a T, N, and M status as well as additional numbers or letters to provide more details about these factors. An overall stage number will be given after categorizing the cancer in this way. There are five stages: stage 0 (zero) and stages I through IV (1 through 4). The stage provides a standardized way of describing the cancer so that doctors can collaborate to plan the best treatment for your colorectal cancer.

Here are the specific details on the TNM staging for colorectal cancer: 

T (Tumor) Categories for Colorectal Cancer

T followed by a letter or number (0 to 4) describes how deeply the primary tumor has grown into the bowel lining. 

TX: The primary tumor cannot be evaluated.

T0: There is no evidence of cancer in the colon or rectum.

Tis: Cancer cells have not grown beyond the colon or rectum's inner layer (mucosa). This is called carcinoma in situ or cancer in situ.

T1: The tumor has grown into the submucosa, the layer of tissue underneath the mucosa or lining of the colon or rectum.

T2: The tumor has grown into the muscularis propria, a deeper, thick muscle layer responsible for moving food down the gut.

T3: The tumor has grown through the outermost layers of the colon or rectum but has not gone through them; it has not reached nearby organs.

T4a: Cancer has grown through all layers of the colon.

T4b: Cancer has grown into or has attached to other organs or structures.

N (Node) Categories for Colorectal Cancer

N followed by a letter or number (0 to 2) indicates whether the cancer has spread to regional lymph nodes near the colon and rectum. 

NX: Regional lymph nodes cannot be evaluated at this time. 

N0: No spread to regional lymph nodes. 

N1a: Cancer cells found in 1 regional lymph node. 

N1b: Cancer cells found in 2 or 3 regional lymph nodes. 

N1c: Tumor cell nodules are present in fat areas near the colon; they are not in the nodes themselves. 

N2a: Cancer cells found in 4 to 6 regional lymph nodes. 

N2b: Cancer cells found in 7 or more regional lymph nodes.

M (Metastasis) Categories for Colorectal Cancer

M followed by a letter or number (0 to 1), describes cancer that has spread to other parts of the body, such as the liver or lungs. This is called distant metastasis.

M0: Cancer has not spread to a distant part of the body.

M1a: Cancer has spread beyond the colon or rectum to 1 other part of the body.

M1b: Cancer has spread to more than 1 part of the body other than the colon or rectum.

M1c: Cancer has spread to distant parts of the peritoneum (the abdominal cavity lining). It may or may not have spread to distant organs or lymph nodes. 

Grade of Colorectal Cancer

The grade (G) also determines the stage of colorectal cancer. It explains how much the cancer cells differ from healthy colon and rectal cells when viewed under a microscope. Cancer cells that resemble normal cells are called "differentiated" or "low-grade tumors." When cancer cells look very different from normal cells, they are called "poorly differentiated" or "high-grade tumors."

GX: The tumor grade cannot be identified.

G1: Well-differentiated cells that look more like healthy cells.

G2: Moderately differentiated cells that look somewhat like healthy cells.

G3: Poorly differentiated cells that look less like healthy cells.

G4: Undifferentiated cells that barely resemble healthy cells.