What is staging?
Not all cancers are alike when they are first diagnosed. Sometimes there’s just a small, single tumor that can be easily removed. Other times, a tumor might be dangerously large or the cancer may have already spread to other parts of the body.
These aren’t trivial differences. The size and extent of cancers when they are first diagnosed reveals a lot of important information about treatment options and future prospects (prognosis). Doctors have developed a system for describing the important details of each newly diagnosed case of cancer. A person’s breast cancer, for instance, might be described as T1 N1 M0. If you’re a cancer patient, becoming familiar with this code will help you understand your disease and your prospects.
The first thing to know about a cancer is where it started. There’s a big difference in treatment for cancer that started in the breast and cancer that started in the skin. After that, doctors can take x-rays, collect tissue samples, run blood tests, or conduct other tests to understand the size and scope of the illness. This process is called staging.
The TNM system: Tumor, lymph nodes, metastasis
Staging a solid tumor typically looks at three major factors: The size of the original tumor, whether the cancer has spread to the lymph nodes, and whether the cancer has spread to other parts of the body. Doctors call this approach the TNM system, and it’s one of the most common staging systems used. The T stands for Tumor size, the N stands for lymph Nodes, and the M stands for metastasis (the medical term for the spread of cancer throughout the body.)
T for tumor size. The size of a tumor is rated on a scale from 0 to 4. If your doctor says you have a T1 tumor, that means that the tumor is small for its type. A T4 tumor would have grown into other neighboring tissue and is often quite large for its type.
- TX: The tumor size can’t be measured
- T0: No primary tumor, or it can’t be found
- Tis: Tumor is “in situ,” meaning it is small and completely contained in the tissue where it started
- T1-4: The tumor is increasing in size and invading surrounding tissues and organs
N for lymph nodes. Lymph is the fluid between all the cells in the body. It collects and flows in lymphatic vessels, and along these vessels are small rounded organs called lymph nodes. Lymph nodes are reservoirs for cells called lymphocytes, the immune cells that produce targeted antibodies and give us long-term immunity against germs and other enemies, including cancer cells. Lymph nodes can intercept and destroy cancer cells that break free of a tumor and migrate to other areas of the body. If they fail to stop the cancer cells, the lymph nodes can end up serving as gateways to the whole body.
The nearby lymph nodes are rated on a scale of 0 to 3. A score of N0 means the lymph nodes are free of cancer. N1 means that a few cancer cells have reached one or more lymph nodes. N3 means that cancer in the lymph nodes is extensive and widespread.
- NX: Nearby lymph nodes can’t be tested or evaluated
- N0: No cancer in nearby lymph nodes, or it can’t be found
- N1-3: Cancer is present in an increasing number of nearby lymph nodes
M for metastasis. An M0 cancer has not spread to other parts of the body, but an M1 cancer has.
- MX: It’s unknown if the cancer has spread
- M0: Cancer has not spread to other parts of the body, or it can’t be found anywhere else
- M1: Cancer has spread to one or more distant parts of the body
So if your cancer is rated T1 N1 M0, you’ll know your prospects look fairly good. The main tumor was small, and although a little bit of cancer was found in your lymph nodes, the disease hasn’t reached other parts of the body.
A T4 N3 M1 cancer would put a person at the opposite end of the spectrum. Even then, a patient’s future would depend on many other factors, including overall health and type of cancer. Cyclist Lance Armstrong had M1 testicular cancer that had spread to his lungs and brain. But after treatment, he managed to beat it back and win the Tour de France an unprecedented seven consecutive times.
For many types of cancer, each TNM rating also matches to a simple stage from zero to four. Doctors often use this staging when talking to patients.
Stage 0 is the earliest type of cancer that has barely begun to grow. Stages I though III include cancers that may have spread to nearby tissues, organs, or lymph nodes, with I being the smallest, least extensive and III being the largest and most extensive. Stage IV (4) includes all cancers that have spread beyond the lymph nodes to more distant parts of the body. For some cancers these stages might be broken down further, and so the Roman numerals would be followed by a letter, for example stage IIIB.
Another system used in major cancer registries uses summary staging, in which cancers are described in one of five terms: “in situ” (still in the original tissue layer), localized (still in the original organ), regional (spread to nearby lymph nodes or other nearby organs), distant (spread to distant body parts), and unknown.
Exceptions to the TNM system
Most cancers fit into the staging system, but there are a few exceptions. Leukemia or other blood-cell cancers can’t be staged because there’s no single solid tumor to measure, and the disease always spreads throughout the body. And staging isn’t very useful for brain cancer because even small tumors can be dangerous if they’re in a vital spot.
There are other staging systems used for these types of cancers, and sometimes childhood cancers and gynecological cancers are staged in different ways as well.
Stage doesn’t generally change
It’s important to understand that staging only applies to the cancer when it’s first diagnosed. The stage doesn’t routinely change over the years, even if the disease gets better or worse. If an M0 cancer eventually spreads to another organ, a doctor will describe it as an M0 cancer that has metastasized. This approach may seem a little confusing, but it helps doctors compare patients and decide on treatments. Think of staging as a first impression.
Tumor cells collected during a biopsy are also checked under a microscope. Cells that look more normal are likely to grow slower; those that look abnormal tend to grow faster. When cells become cancerous, they start to look less distinct or differentiated, with fuzzy edges. The fastest-growing, most malignant cells will not look anything like normal cells. Based on their appearance, the cells are assigned a number from one to four, which is called the tumor grade.
- GX: Grade can’t be evaluated
- G1: Well-differentiated, cells look close to normal (low grade)
- G2: Moderately differentiated, cells look abnormal (intermediate grade)
- G3: Poorly differentiated, cells look very abnormal (high grade)
- G4: Undifferentiated, cells are not distinct at all (high grade)
There are different grading systems used for different types of cancers. The grade affects the outlook for some cancer more than others, so it may or may not make a big difference in your treatment.
National Cancer Institute. Staging: Questions and Answers.
American Cancer Society: Staging.
Nemours Foundation. Spleen and Lymphatic System.
Nobel Prize in Medicine. The Immune System in More Detail.
Cancer Treatment Centers of American. Lymph Nodes.
National Cancer Institute: Tumor Grade: Questions and Answers.
BBC: Lance Armstrong profile.