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.
Stage 0 Colorectal Cancer
Also known as carcinoma in situ, cancer is found only in the innermost lining of the colon or rectum.
Stage I Colorectal Cancer
The tumor has grown into the inner wall of the colon or rectum, but it has not grown through the wall (T1 or T2, N0, M0).
Stage II Colorectal Cancer
Stage IIA: Cancer has grown through the wall of the colon or rectum but has not spread to nearby tissue or the nearby lymph nodes (T3, N0, M0).
Stage IIB: Cancer has grown through the layers of the muscle to the lining of the abdomen, called the visceral peritoneum. It has not spread to the nearby lymph nodes or elsewhere (T4a, N0, M0).
Stage IIC: The tumor has spread through the wall of the colon or rectum and has grown into nearby structures. It has not spread to the nearby lymph nodes or elsewhere (T4b, N0, M0).
Stage III Colorectal Cancer
Stage IIIA: Cancer has grown through the inner lining or into the muscle layers of the intestine. It has spread to 1 to 3 lymph nodes or to a nodule of tumor cells in tissues around the colon or rectum that do not appear to be lymph nodes but has not spread to other parts of the body (T1 or T2, N1 or N1c, M0; or T1, N2a, M0).
Stage IIIB: Cancer has grown through the bowel wall or to surrounding organs and into 1 to 3 lymph nodes or to a nodule of tumor in tissues around the colon or rectum that do not appear to be lymph nodes. It has not spread to other parts of the body (T3 or T4a, N1 or N1c, M0; T2 or T3, N2a, M0; or T1 or T2, N2b, M0).
Stage IIIC: The cancer, regardless of how deep it has grown, has spread to 4 or more lymph nodes but not to other distant parts of the body (T4a, N2a, M0; T3 or T4a, N2b, M0; or T4b, N1 or N2, M0).
Stage IV Colorectal Cancer
Stage IVA: Cancer has spread to a single distant part of the body, such as the liver or lungs (any T, any N, M1a).
Stage IVB: Cancer has spread to more than 1 part of the body (any T, any N, M1b).
Stage IVC: Cancer has spread to the peritoneum and may have spread to other sites or organs (any T, any N, M1c).
Recurrence
Recurrent cancer is cancer that returns after treatment. It can reappear in the colon, rectum, or another part of the body after initial colorectal cancer treatment.
Colorectal Cancer Care in the Willamette Valley
The Willamette Valley Cancer Institute's colorectal cancer specialists offer the most current treatment and are here to customize a treatment plan that works best for you. If you are diagnosed with colorectal cancer, you can schedule an appointment with one of our oncologists at a location convenient to you in Albany, Corvallis, Eugene, Florence, Lincoln City, or Newport, and Springfield, Oregon.
