Colorectal Cancer

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Early Detection, Diagnosis, and Staging TOPICS

Colorectal cancer stages

The stage of a cancer describes the extent of the cancer in the body. The stage is one of the most important factors in deciding how to treat the cancer and determining how successful treatment might be. For colorectal cancer, the stage is based on:

  • How far the cancer has grown into the wall of the intestine
  • If it has reached nearby structures
  • If it has spread to the nearby lymph nodes or to distant organs

The stage of colorectal cancer is based on the results of physical exams, biopsies, and imaging tests (CT or MRI scan, x-rays, PET scan, etc.), which are described in “Tests for colorectal cancer,” as well as the results of surgery.

  • If the stage is based on the results of the physical exam, biopsy, and any imaging tests you have had, it is called a clinical stage.
  • If you have surgery, the results can be combined with the factors used for the clinical stage to determine the pathologic stage.

Sometimes during surgery the doctor finds more cancer than was seen on imaging tests. This can lead to the pathologic stage being more advanced than the clinical stage.

Most patients with colorectal cancer have surgery, so the pathologic stage is most often used when describing the extent of this cancer. Pathologic staging is likely to be more accurate than clinical staging, as it allows your doctor to get a firsthand impression of the extent of your disease.

Understanding your colorectal cancer stage

The staging system most often used for colorectal cancer is the American Joint Committee on Cancer (AJCC) TNM system. The TNM system is based on 3 key pieces of information:

  • How far the main (primary) tumor (T) has grown into the wall of the intestine and whether it has grown into nearby areas.
  • If the cancer has spread to nearby (regional) lymph nodes (N). Lymph nodes are small bean-shaped collections of immune system cells to which cancers often spread first.
  • If the cancer has spread (metastasized) to other organs of the body (M). Colorectal cancer can spread almost anywhere in the body, but the most common sites of spread are the liver and lungs.

Numbers or letters after T, N, and M provide more details about each of these factors. Higher numbers mean the cancer is more advanced. Once a person’s T, N, and M categories have been determined, usually after surgery, this information is combined in a process called stage grouping, and an overall stage of 0, I, II, III, or IV is assigned. Some stages are subdivided with letters.

Stage

Stage grouping

Stage description

0

Tis, N0, M0

The cancer is in its earliest stage. This stage is also known as carcinoma in situ or intramucosal carcinoma (Tis). It has not grown beyond the inner layer (mucosa) of the colon or rectum.

I

T1 or T2, N0, M0

The cancer has grown through the muscularis mucosa into the submucosa (T1), and it may also have grown into the muscularis propria (T2). It has not spread to nearby lymph nodes (N0). It has not spread to distant sites (M0).

IIA

T3, N0, M0

The cancer has grown into the outermost layers of the colon or rectum but has not gone through them (T3). It has not reached nearby organs. It has not yet spread to nearby lymph nodes (N0) or to distant sites (M0).

IIB

T4a, N0, M0

The cancer has grown through the wall of the colon or rectum but has not grown into other nearby tissues or organs (T4a). It has not yet spread to nearby lymph nodes (N0) or to distant sites (M0).

IIC

T4b, N0, M0

The cancer has grown through the wall of the colon or rectum and is attached to or has grown into other nearby tissues or organs (T4b). It has not yet spread to nearby lymph nodes (N0) or to distant sites (M0).

IIIA

T1 or T2, N1, M0

The cancer has grown through the mucosa into the submucosa (T1), and it may also have grown into the muscularis propria (T2). It has spread to 1 to 3 nearby lymph nodes (N1a/N1b) or into areas of fat near the lymph nodes but not the nodes themselves (N1c). It has not spread to distant sites (M0).

OR

T1, N2a, M0

The cancer has grown through the mucosa into the submucosa (T1). It has spread to 4 to 6 nearby lymph nodes (N2a). It has not spread to distant sites (M0).

IIIB

T3 or T4a, N1, M0

The cancer has grown into the outermost layers of the colon or rectum (T3) or through the visceral peritoneum (T4a) but has not reached nearby organs. It has spread to 1 to 3 nearby lymph nodes (N1a or N1b) or into areas of fat near the lymph nodes but not the nodes themselves (N1c). It has not spread to distant sites (M0).

OR

T2 or T3, N2a, M0

The cancer has grown into the muscularis propria (T2) or into the outermost layers of the colon or rectum (T3). It has spread to 4 to 6 nearby lymph nodes (N2a). It has not spread to distant sites (M0).

OR

T1 or T2 N2b, M0

The cancer has grown through the mucosa into the submucosa (T1), and it may also have grown into the muscularis propria (T2). It has spread to 7 or more nearby lymph nodes (N2b). It has not spread to distant sites (M0).

IIIC

T4a, N2a, M0

The cancer has grown through the wall of the colon or rectum (including the visceral peritoneum) but has not reached nearby organs (T4a). It has spread to 4 to 6 nearby lymph nodes (N2a). It has not spread to distant sites (M0).

OR

T3 or T4a, N2b, M0

The cancer has grown into the outermost layers of the colon or rectum (T3) or through the visceral peritoneum (T4a) but has not reached nearby organs. It has spread to 7 or more nearby lymph nodes (N2b). It has not spread to distant sites (M0).

OR

T4b, N1 or N2, M0

The cancer has grown through the wall of the colon or rectum and is attached to or has grown into other nearby tissues or organs (T4b). It has spread to at least one nearby lymph node or into areas of fat near the lymph nodes (N1 or N2). It has not spread to distant sites (M0).

IVA

Any T, Any N, M1a

The cancer may or may not have grown through the wall of the colon or rectum (Any T). It might or might not have spread to nearby lymph nodes. (Any N). It has spread to 1 distant organ (such as the liver or lung) or distant set of lymph nodes (M1a).

IVB

Any T, Any N, M1b

The cancer might or might not have grown through the wall of the colon or rectum. It might or might not have spread to nearby lymph nodes. It has spread to more than 1 distant organ (such as the liver or lung) or distant set of lymph nodes, or it has spread to distant parts of the peritoneum (the lining of the abdominal cavity) (M1b).

Colorectal cancer staging can be complex. If you have any questions about your stage, please ask your doctor to explain it to you in a way you understand.

Explaining the TNM system

T categories for colorectal cancer

T categories of colorectal cancer describe the extent of spread through the layers that form the wall of the colon and rectum. These layers, from the inner to the outer, include:

  • The inner lining (mucosa), which is the layer in which nearly all colorectal cancers start. This includes a thin muscle layer (muscularis mucosa).
  • The fibrous tissue beneath this muscle layer (submucosa)
  • A thick muscle layer (muscularis propria)
  • The thin, outermost layers of connective tissue (subserosa and serosa) that cover most of the colon but not the rectum

Tx: No description of the tumor’s extent is possible because of incomplete information.

Tis: The cancer is in the earliest stage (in situ). It is only in the mucosa and has not grown beyond the muscularis mucosa (thin inner muscle layer).

T1: The tumor has grown through the muscularis mucosa and extends into the submucosa.

T2: The tumor has grown through the submucosa and extends into the muscularis propria (thick outer muscle layer).

T3: The tumor has grown through the muscularis propria and into the outermost layers of the colon or rectum but not through them. It has not reached any nearby organs or tissues.

T4a: The cancer has grown through the serosa (also known as the visceral peritoneum), the outermost lining of the intestines.

T4b: The cancer has grown through the wall of the colon or rectum and is attached to or invades into nearby tissues or organs.

N categories for colorectal cancer

N categories indicate if the cancer has spread to nearby lymph nodes and, if so, how many lymph nodes are involved. To get an accurate idea about lymph node involvement, most doctors recommend that at least 12 lymph nodes be removed during surgery and looked at under a microscope.

Nx: No description of lymph node involvement is possible because of incomplete information.

N0: No cancer in nearby lymph nodes.

N1: Cancer cells are found in or near 1 to 3 nearby lymph nodes

  • N1a: Cancer cells are found in 1 nearby lymph node.
  • N1b: Cancer cells are found in 2 to 3 nearby lymph nodes.
  • N1c: Small deposits of cancer cells are found in areas of fat near lymph nodes, but not in the lymph nodes themselves.

N2: Cancer cells are found in 4 or more nearby lymph nodes

  • N2a: Cancer cells are found in 4 to 6 nearby lymph nodes.
  • N2b: Cancer cells are found in 7 or more nearby lymph nodes.

M categories for colorectal cancer

M categories indicate whether or not the cancer has spread (metastasized) to distant organs, such as the liver, lungs, or distant lymph nodes.

M0: No distant spread is seen.

M1a: The cancer has spread to 1 distant organ or set of distant lymph nodes.

M1b: The cancer has spread to more than 1 distant organ or set of distant lymph nodes, or it has spread to distant parts of the peritoneum (the lining of the abdominal cavity).

Colorectal cancer grades

Another factor that can affect your treatment and your outlook is the grade of your cancer. The grade describes how closely the cancer looks like normal tissue when seen under a microscope.

The scale used for grading colorectal cancers is from 1 to 4.

    · Grade 1 (G1) means the cancer looks much like normal colorectal tissue.

    · Grade 4 (G4) means the cancer looks very abnormal.

    · Grades 2 and 3 (G2 and G3) fall somewhere in between.

The grade is often simplified as either low grade (G1 or G2) or high grade (G3 or G4).

Low-grade cancers tend to grow and spread more slowly than high-grade cancers. Most of the time, the outlook is better for low-grade cancers than it is for high-grade cancers of the same stage. Doctors sometimes use the grade to help decide whether a patient should get additional (adjuvant) treatment with chemotherapy after surgery (discussed in more detail in “Chemotherapy for colorectal cancer”).


Last Medical Review: 10/15/2015
Last Revised: 01/20/2016