- Colon cancer stages range from stage 0 to stage IV.
- The stage is determined using the TNM system: the size or extent of the tumor (T), cancer spread to the lymph nodes (M), and whether the cancer has reached distant sites (N).
- Treatment depends heavily on the stage of cancer.
- Early detection increases the odds of colorectal cancer survival. Because early stages of colorectal cancer don’t have symptoms, regular screening is important.
- At-home screening tests are a safe and convenient alternative to colonoscopy for most people.
Colon cancer stages can be confusing to understand, especially if you’re presented with the information for the first time. Here’s what you should know about the stages of colon cancer and their treatment.
How Are Colon Cancer Stages Determined?
There are two methods of determining colon cancer stages:
- Surgical staging, also called pathological staging. Surgical staging is done in a lab. Tissue is removed from the body and examined for cells, usually after a tumor is removed. Some lymph nodes may also be removed during surgery for testing.
- Clinical staging. Clinical staging uses medical scans, physical exams, and biopsies to determine how far the cancer has spread.
Clinical staging is less invasive, but surgical staging is more accurate.
The TNM System
The most commonly used cancer staging system is called TNM. Colon cancer stages are determined by three factors that are combined to form a staging score, such as T1a N1 M0.
Tumor extent or size (T)
This factor looks at how far the tumor has gotten into the wall of your gastrointestinal tract. The further in, the higher the stage. The tract has four layers:
- The inner lining (mucosa), which has a thin muscle layer where the vast majority of tumors begin.
- The submucosa, fibrous tissue that’s right underneath the mucosa.
- The muscularis propria, a thicker muscle layer responsible for gut motility and moving food.
- And the subserosa and serosa, a thin outer layer of connective tissue. The rectum does not have this layer.
T is measured on a scale of Tis to T4b:
- “is”: Tis is the earliest stage of colon cancer and is only present in the mucosa. It’s often referred to as carcinoma in situ.
- 1: Cancer is present in the mucosa and the submucosa.
- 2: Cancer has grown into the muscularis propria.
- 3: The cancer is present in all layers of the colon or rectum but hasn’t grown through them.
- 4a: The tumor has grown through all layers or reached the abdomen but hasn’t spread to other organs.
- 4b: The cancer is present in nearby organs or tissues.
Spread to Lymph Nodes (N)
N refers to the spread of cancer cells to your lymph nodes, which is usually diagnosed by biopsy. N is measured on a scale of 0 to 2b.
- 0: There is no cancer present in the lymph nodes.
- 1: Cancer is found in one to three nearby lymph nodes.
- 1c: Cancer cells are found in the fat around nearby lymph nodes but not in the nodes.
- 2a: Cancer is found in four to six nearby lymph nodes.
- 2b: There is cancer in seven or more lymph nodes.
Metastasis measures the cancer spread into other organs or to other lymph nodes. Higher stages mean that the cancer has spread to more remote locations. The scale goes from 0 to 1c and includes the following:
- 0: No metastasis.
- 1a: Cancer has spread to one distant organ or to distant lymph nodes.
- 1b: The tumor has spread to more than one distant organ or distant lymph nodes.
- 1c: Cancer is found in distant areas of the abdomen (peritoneum) and may have spread to other distant sites.
In addition, the quality of the cancer cells may play a role in the staging of a tumor. High grade cancer cells look abnormal under a microscope and have a higher chance of spreading quickly than standard cancer cells, resulting in different treatment options.
What Are the Stages of Colon Cancer and Their Treatment?
The treatment of colorectal cancer depends on the stage of the tumor.
Stage 0: Tis, N0, M0
This is the earliest stage and is only found in the mucosa. Stage 0 colon cancer is usually treated with colonoscopic surgery, followed by at-home colon cancer screenings or regular colonoscopies.
Stage I: T1 or T2, N0, M0
The cancer has reached into the submucosa or the muscularis propria but not to nearby lymph nodes or other organs.
Surgical colonoscopy is the first step for a malignant polyp. Once the polyp is removed, it is carefully examined to see if there are cancer cells on the edges. If not, only regular screenings are needed as a next step.
If signs of cancer cells are found on the edge of the polyp, the surgeon wasn’t able to remove the polyp in one piece, or more-advanced cancer cells are found, the next step would be partial colectomy (removing a small piece of the colon).
Stage IIA: T3, N0, M0
The cancer is found in the outermost layers but hasn’t grown through or otherwise spread in the body.
Stage IIA is typically treated with partial colectomy and removal of some lymph nodes for testing to ensure an accurate diagnosis. At this stage, chemotherapy may be under consideration if you have any of these factors:
- The cells found in the tumor are high grade and thus more likely to spread.
- Cancer is found in nearby blood vessels or lymph nodes.
- Fewer than twelve lymph nodes were removed during the surgery.
- Surgeons believe some cancer cells may have been left behind.
- Your colon was obstructed by cancer.
- The cancer caused a perforation, or hole, in your colon.
Stage IIB: T4a, N0, M0
The cancer has grown through the colon but hasn’t spread. Treatment is similar to stage IIA, although chemotherapy is more likely to be used post surgery due to elevated risk of spread.
Stage IIC: T4b, N0, M0
The cancer has grown through and into nearby organs or other tissues but hasn’t spread beyond that. Treatment is similar to stage II tumors with postsurgical chemotherapy to ensure the cancer doesn’t come back. It’s a good idea to consult your doctor about chemotherapy at this stage.
Stage IIIA: T1 or T2, N1/N1c, M0 Or T1, N2a, M0
The designation can mean one of two things: The cancer has spread to four to six nodes but hasn’t been found in distant organs or lymph nodes, or the cancer is found in the submucosa or muscularis propria and has spread to one to three lymph nodes or the fat around them.
Partial colectomy and postsurgical chemotherapy is the standard treatment for stage III. If the tumor is of an unusual size, it may be reduced with radiation to ensure all of the cancer is removed.
Stage IIIB: T3 or T4a, N1/N1c, M0 or T2/T3, N2a, M0 or T1/T2, N2b, M0
Stage IIIB represents three possibilities:
- The cancer has spread through the entire colon or rectum or to the visceral peritoneum, but it hasn’t gone beyond that and has only spread to a couple of lymph nodes.
- Cancer cells have reached the outermost layers and are found in four to six close lymph nodes.
- The cancer has reached the muscularis propria and is found in seven or more lymph nodes.
Surgery is the main approach when treating IIIB. Radiation might be recommended first to shrink the tumor. That may be followed by chemoradiation, a pairing of chemotherapy and radiation therapy, to remove cancer from lymph nodes.
Stage IIIC: T4a, N2a, M0 or T3/T4a, N2b, M0 or T4b, N1/N2, M0
Stage IIIC indicates one of three diagnoses:
- The cancer has gone through the entire colon but hasn’t reached close organs and tissue. It has also been found in four to six lymph nodes but not in distant sites.
- Cancer cells have grown through the colon or through the visceral peritoneum, have spread to seven or more lymph nodes, but haven’t spread beyond that.
- Cancer has reached nearby tissues and organs, has been found in at least one lymph node or fat around the lymph nodes, and hasn’t reached distant sites.
Stage IIIC is treated by partial colectomy, radiation, and chemotherapy. The exact sequence and approach depend on the spread of cells, size of the tumor, and concern over the grade of the cells.
Stage IVA: Any T, Any N, M1a
The cancer has metastasized, meaning it has reached a distant organ, such as the lungs.
Treatment depends on the degree of spread and size of the tumors. It also depends on whether the goal is to extend one’s life or to attempt a cure. In many cases, surgery isn’t a primary treatment as it won’t cure all tumors, although every patient’s situation is different. Generally, some mixture of radiation and chemotherapy is used to attack the multiple tumors, and surgery may be used once the tumors are reduced.
Stage IVB: Any T, Any N, M1b
The cancer has reached more than one distant organ or a distant set of lymph nodes. Treatment is similar to stage IVA cancer.
Stage IVC: Any T, Any N, M1c
The cancer cells have reached distant parts of the lining of the abdominal cavity and might have reached distant organs or lymph nodes. Treatment at this point is decided by long-term outlook and consultation with your oncologist.
Early Detection Is Key
Finding colorectal cancer early is critical to a favorable survival rate, but early stages of colorectal cancer often have no symptoms. Home screening is an affordable and convenient alternative to colonoscopy to detect the first signs of cancer. Learn more about at-home colon cancer test kits, and follow the eDrugstore blog for more information about colorectal cancer.
Dan is a long-time freelance writer focusing on technology, science, health, and medicine, with a lifelong interest in physics, biology, and medicine. His work has taken a particular focus on scientific studies “beyond the headlines,” reading the study to more closely examine the results.