Colorectal Cancer Types & Staging
Colorectal cancer is a collective term used to describe cancer that starts in the colon, rectum, or both. These cancers can also be named colon cancer or rectal cancer, depending on where they start:
Colon Cancer: Type of cancer that begins in the large intestine (colon). The colon is the final part of the digestive tract.
Rectal Cancer: Cancer that begins in the rectum— the last several inches of the large intestine. The rectum starts at the end of the final segment of your colon and ends when it reaches the short, narrow passage leading to the anus.
Most colorectal cancers are adenocarcinomas. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum. Over time, it can spread to lymph nodes as well as other organs including the liver and lungs. When these cancers spread, or metastasize, it is called metastatic colorectal cancer.
Determining the Extent of Colorectal Cancers
If you have been diagnosed with colon cancer, your doctor needs to know the extent (stage) of the disease to plan the best treatment. The stage is based on whether the tumor has invaded nearby tissues, whether the cancer has spread and, if so, to what parts of the body.
Some staging tests your doctor could recommend may include blood tests, colonoscopy, and imaging procedures such as abdominal, pelvic, and chest CT scans. In many cases, the stage of your cancer may not be fully determined until after colon cancer surgery.
While there are many staging systems, the TNM system, created by the American Joint Committee on Cancer (AJCC), is the most widely used.
TNM stands for:
T: the size of the tumor and any spread of cancer into nearby tissue
N: the spread of cancer to nearby lymph nodes
M: metastasis (spread of cancer to other parts of the body)
TX: The primary tumor cannot be evaluated.
T0 (T zero): There is no evidence of cancer in the colon or rectum.
Tis: Refers to carcinoma in situ (also called cancer in situ). Cancer cells are found only in the epithelium or lamina propria, which are the top layers lining the inside of the colon or rectum.
T1: The tumor has grown into the submucosa, which is the layer of tissue underneath the mucosa or lining of the colon.
T2: The tumor has grown into the muscularis propria, a deeper, thick layer of muscle that contracts to force along the contents of the intestines.
T3: The tumor has grown through the muscularis propria and into the subserosa, which is a thin layer of connective tissue beneath the outer layer of some parts of the large intestine, or it has grown into tissues surrounding the colon or rectum.
T4a: The tumor has grown into the surface of the visceral peritoneum, which means it has grown through all layers of the colon.
T4b: The tumor has grown into or has attached to other organs or structures.
NX: The regional lymph nodes cannot be evaluated.
N0 (N zero): There is no spread to regional lymph nodes.
N1a: There are tumor cells found in 1 regional lymph node.
N1b: There are tumor cells found in 2 or 3 regional lymph nodes.
N1c: There are nodules made up of tumor cells found in the structures near the colon that do not appear to be lymph nodes.
N2a: There are tumor cells found in 4 to 6 regional lymph nodes.
N2b: There are tumor cells found in 7 or more regional lymph nodes.
M0 (M zero): The disease has not spread to a distant part of the body.
M1a: The cancer has spread to 1 other part of the body beyond the colon or rectum.
M1b: The cancer has spread to more than 1 part of the body other than the colon or rectum.
M1c: The cancer has spread to the peritoneal surface.
In your pathology report, the stage of your cancer will be indicated by Roman numerals that range from 0 to IV. As a general rule, the lower the number, the less the cancer has spread. By stage IV, the cancer is considered advanced and has spread (metastasized) to other areas of the body.
Doctors also describe colorectal cancer by its grade (G). The grade describes how much cancer cells look like healthy cells when viewed under a microscope. If the cancer looks similar to healthy tissue and has different cell groupings, it is called "differentiated" or a "low-grade tumor." If the cancerous tissue looks very different from healthy tissue, it is called "poorly differentiated" or a "high-grade tumor." Keep in mind that tumors with a lower grade tend to have a better prognosis (outlook) for the patient.
GX: The tumor grade cannot be identified.
G1: The cells are more like healthy cells, called well differentiated.
G2: The cells are somewhat like healthy cells, called moderately differentiated.
G3: The cells look less like healthy cells, called poorly differentiated.
G4: The cells barely look like healthy cells, called undifferentiated.
Stages of Colorectal Cancer
Below is a more detailed breakdown of how your doctor will describe colorectal cancer by its stage:
Stage 0: Also called carcinoma in situ, cancer is found only in the innermost lining of the colon or rectum.
Stage I: The cancer has grown through the mucosa and has invaded the muscular layer of the colon or rectum. It has not spread into nearby tissue or lymph nodes (T1 or T2, N0, M0).
Stage IIA: The cancer has grown through the wall of the colon or rectum but has not spread to nearby tissue or to the nearby lymph nodes (T3, N0, M0).
Stage IIB: The 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 IIIA: The 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: The 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 of the colon, 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 IVA: The cancer has spread to a single distant part of the body, such as the liver or lungs (any T, any N, M1a).
Stage IVB: The cancer has spread to more than 1 part of the body (any T, any N, M1b).
Stage IVC: The cancer has spread to the peritoneum. It may also have spread to other sites or organs (any T, any N, M1c).
Recurrence: This is cancer that has been treated and has returned after a period of time when the cancer could not be detected. The disease may return in the colon or rectum, or in another part of the body.
Treatments Based on Stage and Grade
The treatment plan for colorectal cancer will be largely based on the stage and grade of cancer. Learn more.