Colorectal Cancer1

Colon and rectal cancers begin in the digestive system, also called the gastrointestinal (GI) system. This is where food is processed to create energy and rid the body of solid waste matter (stool).

Colorectal cancer starts in the inner layer of the intestines and can grow through some or all of the other layers. The stage (extent of spread) of a cancer depends to a great degree on how deep the cancer goes into these layers.

In most cases, colorectal cancers develop slowly over many years. We now know that most of these cancers begin as a polyp—a growth of tissue that starts in the lining and grows into the center of the colon or rectum. This tissue may or may not be cancer. A type of polyp known as an adenoma can become cancer. Removing a polyp early may keep it from becoming cancer.

Stage and Grade of Colorectal Cancer2 Staging is used as a guide for prognosis. Stages are often labeled using Roman numerals I through IV (1-4). As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV (4), means a more serious cancer.

There are really two phases to staging for colorectal cancer:

  • Clinical stage—your doctor's best guess of the extent of your disease, based on the results of the physical exam, biopsy, and any other tests you have had prior to surgery.
  • Pathologic stage—this stage is based on what is found during surgery and a biopsy of the tissue after surgery.

Both the clinical and pathologic stages are combined into a TNM staging index. The TNM staging system is a standardized way in which the cancer care team describes the extent of the cancer.

The TNM system describes 3 key pieces of information2:

T describes how far the main (primary) tumor has grown into the wall of the intestine and whether it has grown into nearby areas.

N describes the extent of spread to nearby (regional) lymph nodes. Lymph nodes are small, bean-shaped collections of immune system cells that are important in fighting infections.

M indicates whether the cancer has spread (metastasized) to other organs of the body. (Colorectal cancer can spread almost anywhere in the body, but the most common sites of spread are the liver and lungs.)

Another factor that can affect the outlook for survival is the grade of the cancer. Grade is a description of how closely the cancer looks like normal colorectal tissue under a microscope. Low-grade means the tissue looks more normal; high-grade means the tissue looks less normal. Most of the time, the outlook is not as good for high-grade cancers as it is for low-grade cancers.

In addition, a tumor may be tested for molecular markers. This information is combined with TNM stage and grade to help improve prognostic information.

To learn more about the various tests that Genoptix might perform on colorectal tissue, click here.

1) American Cancer Society. What is colorectal cancer? Accessed 11-18-09.
2) American Cancer Society. How is colorectal cancer staged? Accessed 01-26-10.