Stages of Colorectal Cancer

Executive Summary

The staging system of colorectal cancer helps determine the tumor’s location and its metastasis. The staging system of colorectal cancer uses diagnostic tests. A TNM staging system is used to identify the different stages of colorectal cancer. There are a total of five stages of colorectal cancer, ranging from stage 0 and stage I, stage II (IIA, IIB, and IIC), stage III (IIIA, IIIB, and IIIC) and stage IV (IVA, IVB, and IVC). Recurrent cancer is another stage of cancer that has come back after treatment. The grades in colorectal cancer are categorized as GX, G1, G2, G3 and G4.

Staging System of Colorectal Cancer

Staging is the procedure of determining where the tumor is located, whether it has spread or not, and how it grows. While assessing the colorectal cancer stages, many factors are taken into account. Doctors use diagnostic tests to discover colorectal cancer stages, so staging may not be complete until all tests are finished. 

TNM staging system

The TNM system is the tool doctors use to describe the stage of colorectal cancer. 

• T is for tumor – How large the tumor is and where is its location
• N is for nodes – Has cancer spread to lymph nodes, and if so, where and how many?
• M is for metastasis – Whether cancer has metastasized to other parts of the body.

There are five stages of colorectal cancer – stage 0 (zero) and stages I through IV (1 through 4). 

 T categories for Colorectal cancer

• TX: The primary tumor cannot be evaluated.
• T0 (T plus zero) – Primary cancer in the colon cannot be assessed.
• Tis – Refers to carcinoma in situ. Cancer cells are visible only in the epithelium or the lamina propria, which are the top layers that line the inside of the rectum or colon.
• T1 – The tumor has proliferated into the submucosa, the tissue layer underneath the mucosa of the colon lining.
• T2 –The tumor has grown into the muscularis propria, a more deep, thick layer of muscle that contracts to force along with the contents of the intestines.
• T3 –The tumor has grown through the muscularis propria and into the subserosa, a thin connective tissue layer beneath the outer layer of a few 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 throughout all layers of the colon.
• T4b – The tumor has grown into or has attached to other organs or structures.

 N categories for Colorectal cancer

• NX – The regional lymph nodes cannot be evaluated.
• N0 (N plus 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 formed up of tumor cells found in the structures near the colon that don’t 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.

 M categories for Colorectal cancer

• M0 (M plus zero) – The disease has not spread to a distant part of the body.
• M1a – Cancer has spread to 1 other part of the body beyond the colon or rectum.
• M1b –Cancer has spread to more than 1 part of the body other than the colon or rectum.
• M1c – Cancer has spread to the peritoneal surface.

Grade (G)

Doctors describe this type of cancer by grade. The grade tells how many cancer cells seem healthy when seen under a microscope.

The doctor compares the healthy tissue with cancerous tissue. Healthy tissue comprises many different types of cells grouped. Cancer resembles healthy tissue and has different cell groupings; it is called “differentiated” or a “low-grade tumor.” If the cancerous tissue looks much different from healthy tissue, it is called “poorly differentiated” or a “high-grade tumor”. Colorectal cancer’s grade can help the doctor determine how quickly cancer will spread. In general, the lower the tumor’s grade, the better the prognosis.

• 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.

Cancer stage grouping

The stages of colorectal cancer is determined by combining the results from the TNM system ^​1,2​.

Stage 0 –This is called cancer in situ. The cancer cells are only present in the mucosa, or the inner lining, of the colon or rectum.

Stage I – Cancer has grown through the mucosa and has invaded the muscular layer of the colon or rectum. It has not spread into surrounding tissue or lymph nodes (T1 or T2, N0, M0).

Stage IIA – Cancer has grown through the colon or rectum wall but has not spread to nearby tissue or the nearby lymph nodes (T3, N0, M0).

Stage IIB – Cancer has grown through the muscle layers to the abdominal lining, known as the visceral peritoneum. It has not spread to the surrounding lymph nodes or elsewhere (T4a, N0, M0).

Stage IIC – The tumor has spread through the colon or rectum wall and has grown into nearby structures. It has not spread to the surrounding lymph nodes or elsewhere (T4b, N0, M0).

Stage IIIA – Cancer has grown through the inner lining or into the muscular layers of the intestine. It has spread to 1 to 3 lymph nodes or to a nodule of tumor cells in tissues around the rectum or colon that do not appear to be lymph nodes but has not grown 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 nearby organs and into 1 to 3 lymph nodes or to a nodule of tumor in tissues around the rectum or colon that do not appear to be lymph nodes. It has not spread to other body parts (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 four or more lymph nodes but not to any other distant parts of the body (T4a, N2a, M0; T3 or T4a, N2b, M0; or T4b, N1 or N2, M0).

Stage IVA – Cancer has spread to only one distant part of the body, such as the lungs or liver (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. It can also spread to other sites or organs (any T, any N, M1c).

Recurrent – Recurrent cancer is cancer that has come back after treatment. The disease can be found in the colon, rectum, or another body part. If colorectal cancer returns, there will be another round of tests to know the extent of the recurrence. These tests and scans are usually similar to those at the original diagnosis.

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