Understanding Staging

The stage describes the severity of your cancer and helps your doctor determine whether to recommend additional treatment. The most common system for describing the cancer’s stage, called the TMN classification system, uses a numbering system from I to IV.

For colorectal cancer, stages I and II are typically considered “cured” by surgery and require no further treatment. Stage III patients usually receive additional chemotherapy due to cancer cells that have spread to the lymph nodes near the tumor. Stage IV indicates that the cancer has spread to distant organs.

One of the fuzziest areas in colorectal cancer staging is in stages I and II. When traditional testing methods show no spread of the cancer cells, up to 30% of those patients still have a recurrence of their cancer, indicating that cancer metastases present in the nearby lymph nodes simply may not have been detected. Knowing this statistic, a doctor must balance the risks of possibly under treating and chancing a later recurrence or over treating, which could subject a patient to long-term side effects unnecessarily.

New genetic breakthroughs are offering more sensitive methods of determining the spread of cancer cells to help with this difficult treatment decision. This section explains staging in more detail and helps you understand the risks and options for stage I and II colorectal cancer. Topics include:

Staging Criteria

The American Joint Committee on Cancer (AJCC) developed the TNM classification system for staging. In this system:

  • “T” stands for the size of the tumor and depth of penetration in the colorectal wall.
  • “N” indicates whether the cancer has spread to nearby lymph nodes.
  • “M” indicates whether the cancer has spread to distant regions of the body, usually the lung or liver in the case of colorectal cancer.

TNM Staging Classifications

T
Size and Depth of the Tumor
in the Colorectal Wall		 N
Lymph Nodes Carrying Cancer Cells 		M
Spread (Metastases) to Distant Organs
Tis: Tumor has not grown beyond the inner layer of the colon or rectum (earliest stage) N0: None M0: None
T1: Tumor has invaded the muscular layer of the colon or rectum N1: 1 to 3 lymph nodes M1: Yes (typically the lung or liver)
T2: Tumor grew into the colorectal wall N2: 4 or more lymph nodes  
T3: Tumor grew through the colorectal wall but not into neighboring tissue or organs    
T4: Tumor grew through the colorectal wall and sometimes into nearby tissues or organs    

These factors combine to determine the stage. Following the chart below, for example, a stage II colon cancer would be one that has grown into the colorectal tissue, but it has not spread to nearby lymph nodes and shows no sign of spread to distant organs. If the same patient had cancer cells in the lymph nodes, the cancer would be classified as stage III. In its most detailed form, some stages also have lettered subgroupings that you may encounter, so we outlined them below as well.

Breakdown of Colorectal Cancer Stages

Stage TMN Criteria Description
0 Tis N0 M0 The tumor is still within the inner layer of the colon or rectum. This is also called carcinoma in situ or intramucosal carcinoma. (Also known as Duke A stage.)
I T1 or T2 N0 M0 The tumor is confined within several layers of the colorectal wall and has not spread to nearby tissue or organs. After surgery to remove the tumor, no further treatment is typically provided. (Also known as Duke B stage.)
II       There is no lymph node involvement or spread to distant organs. (Also known as Duke C stage.)
IIA T3 N0 M0 The tumor has grown through the colorectal wall but not to neighboring tissues or organs. After surgery to remove the tumor, no further treatment is typically provided.
IIB T4 N0 M0 The tumor has grown through the colorectal wall and sometimes into neighboring tissues or organs. Many of these patients receive further treatment.
III       Cancer cells have been detected in the lymph nodes, but the cancer has not spread to distant organs. Chemotherapy typically follows surgery. (Also known as Duke D stage.)
IIIA T1 or T2 N1 M0 The tumor is confined to the colorectal wall. Cancer cells have been detected in 1 to 3 lymph nodes, but the cancer has not spread to distant organs.
IIIB T3 N1 M0 The tumor has penetrated the colorectal wall but has not spread to distant organs. Cancer cells were detected in 1 to 3 lymph nodes.
IIIC Any T N2 M0 Cancer cells were detected in 4 or more lymph nodes. The state of the tumor can vary (T1 through T4).
IV Any T Any N M1 The cancer has spread to distant organs. The tumor and lymph node status can vary. Treatment options typically include chemotherapy or radiation. (Also known as Duke E stage.)

Role of Lymph Nodes in Staging

The lymphatic system acts as a filter to prevent foreign bodies from entering your bloodstream. Through a series of lymph nodes located near vital organs, this system traps bacteria and exposes it to immune cells for destruction to prevent infection. Each lymph node is a small, bean-shaped mass, and you may have more or less of these in your body at any given time depending on the immune system activity.

Based on this filtering role, lymph nodes serve as a first point of detection to determine whether cancer cells have left the original tumor site. In the case of colorectal cancer, at the time of surgery, the tumor and surrounding lymph nodes are removed for examination.

Imperfections of Current Lymph Node Analysis Method

The current standard practice is for the hospital pathologist to microscopically examine one or more thin sections of each lymph node for evidence of cancer. This generally involves a 5 µm section of each lymph node, which amounts to less than 1% of the lymph node being sampled for the spread of cancer. This small sample size, therefore, means a lymph node could be deemed cancer free while cells reside in the remaining 99% of the node tissue.

The other risk is that many hospitals are not sampling enough lymph nodes. Several oncology organizations in the U.S. and Canada recommend examining at least 12 lymph nodes. In fact, the National Comprehensive Cancer Network (NCCN) considers examination of less than 12 lymph nodes a risk factor that may influence a doctor’s decision whether or not to treat. Meanwhile, an article in the Journal of the National Cancer Institute (May 28, 2009, online edition) reported that over 60% of nearly 1300 hospitals in the U.S. did not meet this guideline. Therefore, it is important to discuss with your doctor how many lymph nodes are tested and to review your test results to verify that at least 12 nodes were tested.

Breakthroughs in Detecting Colorectal Cancer Spread

While microscopic examination can serve as an initial test, its imperfections may be contributing to the up to 30% of stage I and II patients who are deemed cured (no cancer cells in the lymph nodes) yet experience a recurrence of their cancer later. Fortunately, breakthroughs in genetic testing are opening options to test the lymph nodes with much greater sensitivity.

With the Previstage™ GCC Colorectal Cancer Staging Test, 50% or more of each lymph node is examined using a molecular testing technique. Whereas traditional microscopic examination can detect one cancer cell in 200 normal cells, molecular testing can detect one cancer cell in 10 million normal cells. That’s a 100,000x improvement in sensitivity across a much larger sample of your lymph node, thus significantly increasing the chance of detecting any cancer cells that have spread from the tumor and providing more accurate information for making critical treatment decisions.

Learn more about Previstage™ GCC.