Colorectal Cancer

Diagnosis and Staging

Doctors rely on many tests to diagnose colorectal cancer. Some tests, such as laboratory studies and imaging studies (for example, computerized tomography [CT]), help doctors assign an initial stage to your cancer. This initial stage is known as the clinical stage because it is based on clinical findings. The final stage is assigned by the pathologist who examines the colon or rectal tumor and lymph nodes that were removed during an operation. This final stage is known as the pathologic stage. The stage provides important information for selecting treatment and for predicting the prognosis (outcome).

Colorectal cancer is classified according to the tumor, node, metastasis (TNM) system developed by the American Joint Committee on Cancer (AJCC). 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 are involved (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 AJCC system, a prognostic stage group is assigned. Stages (0 to IV) are further subdivided to group tumors that are associated with similar prognoses. This grouping enables doctors to more accurately predict the outcome according to the stage and to recommend the optimal treatment (Table 2).

The stage of your colorectal cancer and other characteristics of the tumor are documented on a pathology report. Other important information about the tumor includes its histologic grade and the status of the surgical margins. The histologic grade indicates how closely the tumor cells resemble healthy cells. Grade 1 cells look similar to healthy cells, and the tumor is likely to grow slowly; in contrast, grade 4 cells look very different from healthy cells, and the tumor is likely to grow quickly. The surgical margin is the area of healthy tissue around where the tumor was located. The pathologist will examine the margin to see if it contains cancer cells. If cancer cells are present in the margins, additional treatment may be needed. Results of testing for genetic mutations in the tumor are also usually noted on the pathology report.

An accurate diagnosis is crucial to receiving appropriate treatment. Do not be afraid to seek a second opinion about your diagnosis and/or treatment plan.

Table 1. TNM System for Classifying Colorectal Cancer

Classification Definition
Tumor (T)
TX Primary tumor cannot be assessed.
T0 No evidence of primary tumor.
Tis Carcinoma in situ, intramucosal carcinoma (involvement of lamina propria with no extension through muscularis mucosae).
T1 Tumor invades submucosa (second layer of tissue in the colon) (through the muscularis mucosa [first layer of tissue in the colon] but not into the muscularis propria [third layer of tissue in the colon]).
T2 Tumor invades the muscularis propria (third layer of tissue in the colon).
T3 Tumor invades through the muscularis propria (third layer of tissue in the colon) into pericolorectal tissues (tissues around the colon and rectum).
T4

   T4a



   T4b
Tumor invades the visceral peritoneum (outer lining of colon or rectum) or invades or adheres to adjacent organ or structure.
Tumor invades through the visceral peritoneum (outer lining of colon or rectum) (including gross perforation of the bowel through tumor and continuous invasion of tumor through areas of inflammation to the surface of the visceral peritoneum).
Tumor directly invades or adheres to adjacent organs or structures.
Node (N)
Nx
Regional lymph nodes cannot be assessed.
N0
No regional lymph node metastasis.
N1


   N1a
   N1b
   N1c
One to three regional lymph nodes are positive (tumor in lymph nodes measuring greater than or equal to 0.2 mm), or any number of tumor deposits are present and all identifiable lymph nodes are negative.
One regional lymph node is positive.
Two or three regional lymph nodes are positive.
No regional lymph nodes are positive, but there are tumor deposits in the subserosa, mesentery or nonperitonealized pericolic, or perirectal/mesorectal tissues (nearby tissues).
N2
   N2a
   N2b
Four or more regional nodes are positive.
Four to six regional lymph nodes are positive.
Seven or more regional lymph nodes are positive.
Metastasis (M)
M0
No distant metastasis by imaging, etc.: no evidence of tumor in distant sites or organs.
M1

   M1a

   M1b

   M1c
Metastasis to one or more distant sites or organs or peritoneal (membrane that lines the abdominal cavity) metastasis is identified.
Metastasis to one site or organ is identified without peritoneal (membrane that lines the abdominal cavity) metastasis.
Metastasis to two or more sites or organs is identified without peritoneal (membrane that lines the abdominal cavity) metastasis.
Metastasis to the peritoneal (membrane that lines the abdominal cavity) surface is identified alone or with other site or organ metastases.

Table 2. Stages of Colorectal Cancer

 Stage  T  N  M
0 Tis N0 M0
I T1
T2
N0
N0
M0
M0
IIA T3 N0 M0
IIB T4a N0 M0
IIC T4b N0 M0
IIIA T1-T2
T1
N1/N1c
N2a
M0
M0
IIIB T3-T4a
T2-T3
T1-T2
N1/N1c
N2a
N2b
M0
M0
M0
IIIC T4a
T3-T4a
T4b
N2a
N2b
N1-N2
M0
M0
M0
IVA Any T Any N M1a
IVB Any T Any N M1b
IVC Any T Any N M1c

Used with permission of the American Joint Committee on Cancer (AJCC), Chicago, Illinois. The original and primary source for this information is the AJCC Cancer Staging Manual, Eighth Edition (2017) published by Springer Science+Business Media.

Additional Sources of Information

 

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