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Staging Colorectal Cancer

Staging, Tests, Biopsies and Grading

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Updated December 22, 2011

After hearing you have colon cancer, the very first question to leave your lips might be, "How bad is it?"

Learning you have cancer is only the first piece of the puzzle. The other pieces, such as pathology reports or blood and X-ray tests, will complete the picture and help your doctor determine the stage and grade of your cancer. Your doctor needs to know how extensive your cancer is before he or she can help you treat it.

What Is Staging?

The term staging is used to describe how early the cancer has been caught and if it has metastasized (spread) to other parts of the body. In the very early stages, the cancerous cells are usually contained to one small section of bowel, such as an isolated polyp, and have not spread to surrounding tissues. Later stages of colon cancer have spread outside of the bowel, potentially to other organs such as the lungs or liver.

How Staging Works

A variety of tests – X-rays, blood, nuclear medicine – will help your doctor determine if the cancer is isolated within the innermost lining of the colon, or if it has spread outside of your colon and to what extent it has spread.

Blood testing may include a complete blood count (CBC), chemistries and carcinoembryonic antigen (CEA) levels. Whereas the CBC and chemistry tests can give a general picture of overall health, the CEA levels provide a baseline measurement of special, cancer-only proteins present in your body before treatment. These proteins are called tumor markers. There are different types of protein tumor markers that may be tested, including CA 19-9 (specific to intestinal and pancreatic cancers) and alkaline phosphatase (specific to liver or bone metastasis).

Diagnostic imaging tests may include simple X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. These imaging procedures are painless, yet thorough.

  • A chest X-ray is a simple tool, giving a black-and-white, two-dimensional picture of the body. They are fast, painless and can help detect if the cancer has spread outside of the colon to the lungs (lung metastasis).

  • CT scans are like a three-dimensional X-ray, giving the doctor a better interpretation of the size and location of any tumors in the colon or throughout the body.

  • An MRI creates highly detail, three-dimensional pictures without the radiation exposure of a CT scan. However, an MRI may take longer and cannot be used for people with metal or metallic implants including pacemakers or surgical clips.

  • PET scans are potentially useful to clarify findings in a CT scan. To perform a a PET scan, tiny amounts of radioactive glucose (sugar) are injected through an intravenous line. Large pockets of cancerous cells soak up this sugar and become more visible on the scan. Thus if an irregularity is found on a CT scan, the amount of uptake of radioactive sugar might confirm the irregularity to be cancer.

A biopsy of irregular tissue will determine if the colon cancer has spread to other parts of the body. A doctor who specializes in microscopic tissue specimens and diagnosis, called a pathologist, will look at the cells retrieved during the biopsy to determine if they are cancerous or not. If the cells are cancerous, the pathologist will further determine if they came from the colon cancer (metastasized) or if they are a completely separate cancer that has formed.

Grading the Cancer

Your cancer grade is not the same as its stage. The grade of cancer determines how aggressive the cancerous cells are and potentially how likely they are to spread. The pathologist determines the grade of cancer while looking at the biopsy samples under a microscope. Cancerous cells may be slightly abnormal in appearance and still resemble normal colon tissue (low-grade); completely abnormal in appearance (high-grade); or somewhere in between. The doctor takes the grading of the cancer into account when he or she gives you a prognosis (prediction) of how well you will recover from the cancer.

Staging Systems

Once he or she knows the extent of metastasis (if any), your doctor will use a system of numbers, letters or a combination of both to stage your colon cancer. There are three staging systems used to classify colorectal cancers:
  • TNM Staging – Uses the letters T (primary colon tumor), N (lymph node) and M (metastasis). The overall severity is then determined to provide a numeric staging (0-IV)

  • Duke’s Staging – One of the first staging systems. Uses the letters A, B and C to identify cancer stage and metastasis

  • Astler-Coller – Based on Duke’s staging, this system includes various degrees of metastasis, measured in numbers, to accompany the letters A through D

Although some doctors continue to use both Duke’s and Astler-Coller staging systems, the most widely accepted staging system is the TNM system.

Colon Cancer Stages: TNM System

In the TNM staging system, the letters T, N and M are followed by a number that lends further description of the cancer’s growth and spread.
  • The number following the letter T is used to describe the original colon tumor and depict how far it has invaded into the tissues of the colon. This is usually represented as T1 through T4, with a few exceptions.

  • The number following the letter N depicts lymph node involvement. (N0 represents no lymph involvement; N1 or N2 shows that lymph nodes are involved.)

  • The number following the letter M represents a metastasis. (M0 is no metastasis; M1 represents metastasis to another site, such as the lungs or liver.)

Stage 0 (Tis, N0, M0) or carcinoma in situ (Tis - Tumor in Situ): the cancer has not spread past the innermost lining of your colon.

Stage I (T1, N0, M0 or T2, N0, M0): the cancer made it past the inner lining or it has entered the muscular layer of the colon, but has not penetrated outside the colon.

Stage IIA (T3, N0, M0): the cancer has extended all the way through the walls of the colon, but not spread to the outside of it.

Stage IIB (T4, N0, M0): the cancer has extended through the wall of the colon, possibly outside, but has not invaded nearby tissues.

Stage IIIA (T1 or T2, N1, M0): the cancer stopped at the walls of the colon but has spread to lymph nodes nearby.

Stage IIIB (T3 or T4, N1, M0): the cancer has extended through the wall of the colon and spread to lymph nodes nearby.

Stage IIIC (T3 – T4, N2, M0): the cancer has potentially spread to nearby organs or tissues, lymph nodes, and has grown through the layers of the colon.

Stage IV (T3 –T4, N1 – N2, M1): the cancer has metastasized to organs or tissues that are not adjacent to the colon (the lungs, for instance).

There are further subdivisions of the colon cancer stages and elements, such as stage IVA or N2a, which go into further depth describing the cancer. Talk to your doctor if you don't understand how your cancer has been staged. The stage of your cancer is directly related to how your doctor will implement a treatment plan. Taking an active part in understanding your colon cancer staging may empower you throughout your treatment.

Sources:

American Cancer Society. (n.d.). How is Colorectal Cancer Staged? Accessed December 7, 2011.

Lange, V. (2004). Be a survivor. colorectal cancer treatment guide. (4th ed.). Los Angeles: Lange Productions.

Fintel, W. A., & McDermott, G. R. (2004). Cancer -- a medical and spiritual guide for patients and their families. Grand Rapids, MI: Baker Books.

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