If a colon polyp or cancer has been discovered on a colonscopy, your medical team may perform many tests to classify the stage and grade of colorectal cancer. Staging and grading are universal systems to describe, evaluate and compare a particular cancer and its treatments, so that health professionals can communicate on the same level across the world.
As is displayed below, polyps have the potential to turn into cancer if they remain in the colon for a long period of time as shown below. This process is discussed in great detail in the section From Polyps to Cancer.
Adenomatous polyps and adenocarcinoma are epithelial tumors of the large intestine, and the most common and clinically significant of intestinal neoplasms. The potential for polyps or adenomas to develop into cancer increases with the age of the patient. Adenomas larger than one centimeter, with extensive villous patterns, have an increased risk of developing into carcinomas.
|Progression from Polyp to Cancer|
The vast majority of colorectal cancers are adenocarcinomas, tumors that arise from the mucosa cells of the colon. While most adenocarcinomas are well or moderately differentiated, approximately 15% are poorly or undifferentiated tumors. These tumors are associated with a poorer prognosis. Mucinous or colloid carcinomas, with moderate to prodigious mucin production, are also associated with less favorable five-year survival rates.
Staging of Colorectal Cancer
Staging of colorectal cancer refers to how far a cancer has spread on a scale from 0 to IV, with 0 meaning a cancer that has not begun to invade the colon wall and IV describing cancer that has spread beyoned the original site to other parts of the body.
Tumors are staged or graded for severity, according to evidence of invasion into the intestinal wall, or evidence of spread. There is a close correlation between advancing stage and cancer mortality. Tumor size does not appear to be important in terms of outcome. The aggressiveness of colorectal cancer is based upon its ability to grow and invade the colonic wall, lymphatic system, and blood vessels.
Your doctor may not be able to determine the stage or grade of your cancer until after surgery, when the tumor has been examined by a pathologist.
The Staging System describes whether the cancer is:
- in the inner linining of the colon only
- embedded in the colon wall
- penetrating through the colon wall
- involving lymph nodes
- metastatic (spread to other organs)
The prognosis for colorectal cancer patients depends on the extent of disease and the adequacy of the surgical procedure. Patients have a worse prognosis if the cancer has spread to the lymph nodes or distant organs, has invaded blood and lymphatic vessels, or is poorly differentiated. Colorectal cancer is called a metastatic disease when the cancer has spread from the colon or the rectum to another part of the body. Colorectal cancer most commonly spreads to the liver or the lungs.
Although staging of your cancer is is an important indication of the type of treatment you may receive, it is not the sole factor in defining your specific treatment. All treatment decisions at Johns Hopkins are determined on an individual basis, because no two cancers and no two people are identical. Several other factors are considered in your individual assesment, including your age, general health, family history of cancer, other medical conditions, and whether it is a new cancer or one that has recurred. Since each patients situation is unique, you should ask your doctor for a detailed explanation of the implications of the stage of your cancer.
Classification of Tumor Spread
Doctors use two staging systems to define the extent of invastion of colorectal cancer: the Dukes' classification and the TNM staging staging system. In both systems, carcinoma in situ (also referred to as high grade dysplasia) is defined as intramucosal carcinoma that does not penetrate the muscularis mucosae.
TNM Staging System
The TNM System, developed by the American Joint Committee on Cancer (AJCC) is the most widely used, and is considered the most precise and descriptive. T stands for tumor and the depth to which it has penetrated the colon wall, N stands for lymph node involvement, and M refers to metastases, or whether the cancer has spread to other body parts.
|A comparision of TNM and Dukes' Classification |
Key for TNM Staging
Primary Tumor (T)
TX – primary tumor cannot be assessed
T0 – no evidence of primary tumor
Tis – carcinoma in situ: intraepithelial or invasion of lamina propria
T1 – tumor invades submucosa
T2 – tumor invades muscularis propria
T3 – tumor invades through muscularis propria into subserosa or into nonperitonealized pericolic or perirectal tissues
T4 – tumor directly invades other organs or structures and/or perforates visceral peritoneum
Regional Lymph Nodes (N)
NX – regional lymph nodes cannot be assessed
N0 – no regional lymph node metastasis
N1 – metastasis in one to three regional lymph nodes
N2 – metastasis in four or more regional lymph nodes
Distant Metastases (M)
MX – distant metastasis cannot be assessed
M0 – no distant metastasis
M1 – distant metastasis
|TNM classification of colorectal cancer stages.|
Dukes’ Classification (Astler-Coller modification)
|tumors invade through the muscularis mucosae into the submucosa but do not reach the muscularis propria|
|Stage B1 ||tumors invade into the muscularis propria|
|Stage B2 ||tumors completely penetrate the smooth muscle layer into the serosa|
|Stage C ||tumors encompass any degree of invasion but are defined by regional lymph node involvement|
|Stage C1 ||tumors invade the muscularis propria with fewer than four positive nodes|
|Stage C2 ||tumors completely penetrate the smooth muscle layer into the serosa with four or more involved nodes|
|Stage D ||lesions with distant metastases |
|Carcinoma in situ ||(may be referred to as high grade dysplasia) – intramucosal carcinoma that does not penetrate the muscularis mucosae|