Cancer Staging is the process of finding out how much cancer is in a person’s body and where it’s located. It’s how the doctor determines the stage of a person’s cancer.
For most types of cancer, doctors use staging information to help plan treatment and to predict a person’s outlook (prognosis). Although each person’s situation is different, cancers with the same stage tend to have similar outlooks and are often treated the same way. The cancer stage is also a way for doctors to describe the extent of the cancer when they talk with each other about a person’s cancer.
Why is staging needed?
Doctors need to know the amount of cancer and where it is in the body to be able to choose the best treatment options. For example, the treatment for an early-stage cancer may be surgery or radiation, while a more advanced-stage cancer may need to be treated with chemotherapy. Doctors also use a cancer’s stage to help predict the course it will likely take.
In a larger sense, doctors use staging information when they’re studying cancer treatments. It allows researchers to make sure study groups are actually similar when they test cancer treatments against one another, measure outcomes, and more.
Not all cancers are staged. For example, leukemias are cancers of the blood cells and therefore spread throughout the body. Most types of leukemias aren’t staged the way cancers that form tumors are.
What is the doctor looking for when staging cancer?
When trying to determine the extent of the cancer in the body, doctors first look at the primary (main) tumor for its size, location, and whether it has grown into nearby areas. Doctors also check for other nearby tumors.
Doctors might also look at nearby lymph nodes to find out if cancer has spread into them. Lymph nodes are small, bean-shaped collections of immune cells. Many types of cancer often spread to nearby lymph nodes before they reach other parts of the body.
Doctors might also look at other parts of the body to see if the cancer has spread there. When cancer spreads to parts of the body far from the primary tumor, it is known as metastasis.
In some kinds of cancer, other factors are also used to help determine the stage, such as the cancer cell type and grade (how abnormal the cancer cells look under a microscope), or the results of certain blood tests.
How are cancers staged?
Doctors use different types of exams and tests to figure out a cancer’s stage. Depending on where the cancer is located, the physical exam may give some clue as to how much cancer there is. Imaging tests like x-rays, CT scans, MRIs, ultrasound, and PET scans may also give information about how much and where cancer is in the body.
A biopsy often is needed to confirm a cancer diagnosis. Biopsies might also be needed to find out if an abnormal spot seen on an imaging test is really cancer spread. During a biopsy, the doctor removes a tumor or pieces of a tumor to be looked at under a microscope. Some biopsies are done during surgery. But with many types of biopsies, the doctor removes small pieces of tumor through a thin needle or through a flexible lighted tube called an endoscope. The different kinds of biopsies used to check for cancer are described in Cancer Surgery.
Types of staging
Staging is done when a person is first diagnosed, before any treatment is given. The main types of staging are:
This is an estimate of the extent of the cancer based on results of physical exams, imaging tests (x-rays, CT scans, etc.), and tumor biopsies. For some cancers, the results of other tests, such as blood tests, are also used in staging.
The clinical stage is a key part of deciding the best treatment to use. It’s also the baseline used for comparison when looking at how the cancer responds to treatment.
If surgery is being done, doctors can also determine the pathologic stage (also called the surgical stage) of the cancer. The pathologic stage relies on the results of the exams and tests mentioned before, as well as what is learned about the cancer during surgery. Often this is surgery to remove the cancer and nearby lymph nodes, but sometimes surgery may be done to just look at how much cancer is in the body and take out tissue samples.
Sometimes, the pathologic stage is different from the clinical stage (for instance, if the surgery shows the cancer has spread more than was thought). The pathologic stage gives the health care team more precise information that can be used to predict treatment response and outcomes (prognosis).
There are different types of staging systems, but the most common and useful staging system for most types of cancers is the TNM system.
The TNM system
The American Joint Committee on Cancer (AJCC) and the International Union for Cancer Control (UICC) maintain the TNM classification system as a tool for doctors to stage different types of cancer based on certain standards. It’s updated every 6 to 8 years to include advances in our understanding of cancer.
In the TNM system, each cancer is assigned a letter or number to describe the tumor, node, and metastases.
- T stands for the original (primary) tumor.
- N stands for nodes. It tells whether the cancer has spread to the nearby lymph nodes
- M stands for metastasis. It tells whether the cancer has spread to distant parts of the body
The T category gives information about aspects of the original (primary) tumor, such as its size, how deeply it has grown into the organ it started in, and whether it has grown into nearby tissues.
- TX means the tumor can’t be measured.
- T0 means there is no evidence of a primary tumor (it cannot be found).
- Tis means that the cancer cells are only growing in the most superficial layer of tissue, without growing into deeper tissues. This may also be called in situ cancer or pre-cancer.
- Numbers after the T (such as T1, T2, T3, and T4) might describe the tumor size and/or amount of spread into nearby structures. The higher the T number, the larger the tumor and/or the more it has grown into nearby tissues.
The N category describes whether the cancer has spread into nearby lymph nodes.
- NX means the nearby lymph nodes cannot be evaluated.
- N0 means nearby lymph nodes do not contain cancer.
- Numbers after the N (such as N1, N2, and N3) might describe the size, location, and/or the number of nearby lymph nodes affected by cancer. The higher the N number, the greater the cancer spread to nearby lymph nodes.
The M category tells whether the cancer has spread (metastasized) to distant parts of body).
- M0 means that no distant cancer spread was found.
- M1 means that the cancer has spread to distant organs or tissues (distant metastases were found).
Most cancer types have their own version of this classification system, so letters and numbers don’t always mean the same thing for every kind of cancer. For example, in some types of cancer, the T categories describe the size of the main tumor, while in others they describe how deeply the tumor has grown in to the organ it started in, or whether the tumor has grown into nearby structures (regardless of its size).
Some cancer types also have special groupings that are different from other cancer types. For instance, for some cancers, classifications may have subcategories, such as T3a and T3b, while others may not have an N3 category.
Once the values for T, N, and M have been determined, they are combined to assign an overall stage. For most cancers, the stage is a Roman numeral from I to IV, where stage IV (4) is the highest and means the cancer is more advanced than in the lower stages. Sometimes stages are subdivided as well, using letters such as A and B.
Stage 0 is carcinoma in situ for most cancers. This means the cancer is at a very early stage, is only in the area where it first developed, and has not spread. Not all cancers have a stage 0.
Stage I cancers are the next least advanced and often have a good prognosis (outlook). The outlook is usually not as good for higher stages.
Other factors that can affect the stage
For some cancers, the values for T, N, and M aren’t the only things that determine the stage. Some other factors that may be taken into account include:
Grade: For most cancers, the grade is a measure of how abnormal the cancer cells look under the microscope. This is called differentiation. Grade can be important because cancers with more abnormal-looking cells tend to grow and spread faster.
The grade is usually assigned a number. In low-grade (well-differentiated) cancers, the cancer cells look a lot like cells from normal tissue. In general, these cancers tend to grow slowly. In high-grade (poorly differentiated) cancers, the cancer cells look very different from normal cells. High-grade cancers often tend to grow quickly and have a worse outlook, so they may need different treatments than low-grade cancers. Even when the grade doesn’t affect a cancer’s stage, it may still affect the outlook and/or treatment.
Cell type: Some cancers can be made up of different types of cells. Because the type of cancer cell can affect treatment and outlook, it can be a factor in staging. For example, cancers of the esophagus are mainly either squamous cell cancers or adenocarcinomas. Squamous cell esophageal cancers are staged differently from esophageal adenocarcinomas.
Tumor location: For some cancers, the tumor’s location affects outlook and is taken into account in staging. The stage of cancer of the esophagus, for example, depends on whether the cancer is in the upper, middle, or lower third of the esophagus.
Tumor marker levels: For some cancers, the blood levels of certain substances (called tumor markers) can affect the stage of the cancer. For example, in prostate cancer, the level of prostate-specific antigen (PSA) in the blood is taken into account in assigning a stage.
Other staging systems
Not all cancers are staged using the TNM system. Some cancers grow and spread in a different way. For example, many cancers in or around the brain are not staged using the TNM system, since these cancers tend to spread to other parts of the brain and not to lymph nodes or other parts of the body. Staging systems other than the TNM system are often used for Hodgkin disease and other lymphomas, too, as well as for some childhood cancers.
The International Federation of Gynecologists and Obstetricians (FIGO) has a staging system for cancers of the female reproductive organs. The TNM stages closely match the FIGO stages, which makes it fairly easy to convert stages between these 2 systems.
Other, older staging systems (such as the Dukes system for colorectal cancer) may still be used by some doctors. If your doctor uses another staging system, you may want to find out if the stage can be translated into the TNM system. This will often help if you want to read more about your cancer and its treatment, since the TNM system is more widely used.
A cancer’s stage does not change
An important point some people have trouble understanding is that the stage of a cancer is determined only when (or soon after) the cancer is diagnosed. This stage does not change over time, even if the cancer shrinks, grows, spreads, or comes back after treatment. The cancer is still referred to by the stage it was given when it was first found and diagnosed, although information about the current extent of the cancer is added (and of course, the treatment is adjusted as needed).
For example, let’s say a woman is first diagnosed with stage II breast cancer. The cancer goes away with treatment, but then it comes back and has spread to the bones. The cancer is still called a stage II breast cancer, now with recurrent disease in the bones.
If the breast cancer did not go away with the original treatment and spread to the bones it would be called a stage II breast cancer with bone metastasis. In either case, the original stage does not change and it’s not called a stage IV breast cancer. Stage IV breast cancer refers to a cancer that has already spread to a distant part of the body when it’s first diagnosed.
This is important to understand because survival statistics and information on treatment by stage for specific cancer types refer to the stage when the cancer was first diagnosed. The survival statistics related to stage II breast cancer that has recurred in the bones may not be the same as the survival statistics for stage IV breast cancer.
At some point you may hear the term “restaging.” Restaging is a term sometimes used to describe doing tests to find the extent of the cancer after treatment. This is rarely done, but it may be used to measure the cancer’s response to treatment or to assess cancer that has come back (recurred) and will need more treatment. Often the same tests that were done when the cancer was first diagnosed (such as physical exams, imaging tests, biopsies, and maybe surgery) will be done again. After these tests a new stage may be assigned. It’s written with a lower-case “r” before the new stage to note that it’s different from the stage at diagnosis. The originally diagnosed stage always stays the same. While testing to see the extent of cancer is common during and after treatment, actually assigning a new stage is rarely done, except in clinical trials.