Advanced Colorectal Cancer

Staging

Identifying the stage of colorectal cancer is essential for determining the prognosis (likely outcome after treatment) and for planning the best possible treatment approach. Staging also helps doctors describe where the cancer is located, if and where it has spread, and whether other organs in the body are affected by it.

Colorectal cancer is usually staged twice. First, your doctor will evaluate the results of your physical exam, laboratory tests and imaging tests (see Detection) and assign a clinical stage. Then, after a staging procedure or surgical resection is done, a pathologist will examine tissue taken from the tumor and nearby lymph nodes and assign a pathologic stage, which provides more details about the cancer. The enhanced accuracy of the pathologic stage is important to determine the best treatment options and predict the prognosis.

Colorectal cancer is classified according to the tumor, node, metastasis (TNM) system developed by the American Joint Committee on Cancer and the International Union against Cancer. For many cancers, the size and location of the tumor is of critical importance, but for colorectal cancer, how deeply the tumor penetrates the layers of the intestine is the most important feature of the tumor. The T category is used to describe this depth, the N category is used to describe how many nearby lymph nodes contain cancer cells and the M category is used to note whether cancer has metastasized (spread) to other parts of the body (Table 1). Once a colorectal cancer has been classified with the TNM system, an overall stage is assigned (Table 2). Stages III and IV are considered advanced disease.

Table 1. TNM classification for colorectal cancer

Classification Definition
Tumor (T)
Tx Tumor cannot be evaluated (because of lack of information)
T0 No evidence of primary tumor
Tis Carcinoma in situ; cancer cells are found only in the mucosa (the first layer, or inner lining, of the colon or rectum)
T1 Tumor has grown into the submucosa (the second layer of the colon or rectum)
T2 Tumor has grown into the muscularis propria (the third layer of the colon or rectum)
T3 Tumor has grown into the subserosa (the deepest layer of the colon or rectum)
T4a Tumor has grown through the entire wall of the colon
T4b Tumor has invaded or is adherent to nearby tissues or organs
Nodes (N)
Nx Nearby lymph nodes were not evaluated
N0 No cancer cells are found in nearby lymph nodes
N1a Cancer cells are found in one nearby lymph node
N1b Cancer cells are found in two or three nearby lymph nodes
N1c Cancer cells are found in the subserosa, mesentery (the fatty tissue that contains the lymph nodes and blood vessels) or tissues around the colon or rectum but not in nearby lymph nodes
N2a Cancer cells are found in four, five or six nearby lymph nodes
N2b Cancer cells are found in seven or more nearby lymph nodes
Metastasis (M)
M0 Cancer has not spread beyond nearby lymph nodes
M1a Cancer is detected in one organ or site (for example, in the liver, lung, ovary or distant lymph node)
M1b Cancer is detected in more than one organ or site or in the peritoneum lining (the lining of the abdominal cavity)

 

Colorectal cancers are also graded. The grade refers to how closely the cancer cells resemble normal cells under a microscope. The scale ranges from 1 to 4, with 1 representing cancer cells that look similar to normal cells and 4 representing cancer cells that look vastly different from normal cells. Generally, the lower the grade, the better the outlook for the patient.

Table 2. Stages of advanced colorectal cancer

Stage TNM classifications
Stage IIIa
T1 or T2, N1(a-c), M0
T1, N2a, M0
Stage IIIb
T3 or T4a, N1(a-c), M0
T2 or T3, N2a, M0
T1 or T2, N2b, M0
Stage IIIc
T4a, N2a, M0
T3 or T4a, N2b, M0
T4b, N1(a-c) or N2, M0
Stage IVa
Any T, any N, M1a
Stage IVb
Any T, any N, M1b

 

Sites of metastasis

In Stage IV colorectal cancer, the disease has metastasized to at least one other place in the body. Colorectal cancer can spread beyond the colon or rectum in one of three ways:

  1. The tumor can invade directly into the wall of the colon and surrounding tissue.
  2. Cancer cells can break off from the tumor and travel through the lymph system to lymph nodes in the area of the tumor.
  3. Cancer cells can enter small blood vessels and travel through the body via the bloodstream.

The most common sites of metastasis in colorectal cancer include the liver, the lungs and the peritoneum, which is the tissue that lines the abdominal wall and covers most of the organs in the abdomen.

 

Additional Resources

 

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