Stages of Cancer
What are cancer stages?
The stage of a cancer describes the size of the original cancer, known as the primary site or tumor, and whether it has spread, either to nearby lymph nodes or to other parts of the body.
- It helps to determine the severity of the cancer
- Knowing the stage of a cancer enables healthcare providers to formulate a more effective treatment plan
- The stage can be used to provide a prognosis: a forecast of the likely course of the condition, based on other, similar, cases with the same stage
- It can help to predict the chances of the cancer returning, known as recurrence or relapse after the first treatment
- It is important in identifying clinical trials that may be suitable for that person’s treatment
- Staging enables doctors to talk about the diagnosis in a clear, common language
- It can help to determine how well treatment has worked
Cancer first develops in one cell, which grows and divides without dying, and normally forms a tumor, a mass of cells in one area of the body. As the tumor grows, cancer may invade nearby tissues and organs.
Cells of the tumor may also break away and enter the bloodstream or the lymphatic system, which carries lymph, a fluid that helps to fight infection. From there, the cancerous cells can spread from the primary tumor to lymph nodes or to other organs and may form new tumors. The spread of cancer from the primary site to other parts of the body is known as metastasis.
There are two main types of systems for staging cancer:
- The Tumor Node Metastasis (TNM) system
- The number system
TNM staging is used to classify almost all solid tumors, sometimes in combination with the number system. Other cancers, such as blood or brain cancers, may have their own classification systems, which are often based on the TNM classification.
Tumor Node Metastasis (TNM) staging
- T refers to the size and extent of the original tumor, also known as the primary tumor.
- N refers to whether and to what extent the cancer has spread to nearby lymph nodes, known as regional lymph nodes.
- M refers to whether and how extensively the cancer has spread to other parts of the body, known as distant metastasis.
A number or letter is added to T, N and M, to describe the findings for each. Once the T, N and M are determined, for many cancers they may be converted into the number system by being given a number between I to IV – the Roman numerals for 1 to 4 – or a 0 (see the 5 cancer stages of the number system).
T: Primary tumor
- TX: The original tumor cannot be assessed.
- T0: The original tumor cannot be found.
- Tis: Abnormal cells are present, but have not infiltrated neighboring tissue. Some doctors do not consider this to be cancerous, but rather precancerous with the potential to become cancer. It is also known as carcinoma in situ (CIS).
- T1, T2, T3, T4: This refers to the size and/or extent of the original tumor. The higher the number, the larger the tumor, or the more it has invaded nearby tissues. A T may be further divided to provide more detail, for instance, T2a or T2b.
N: Regional lymph nodes
- NX: The nearby lymph nodes cannot be assessed.
- N0: The cancer has not spread to nearby lymph nodes.
- N1, N2, N3: This refers to the number and location of nearby lymph nodes that contain cancer. Normally, the higher the number, the more lymph nodes. Often the number also describes the location of the affected lymph nodes.
M: Distant metastasis
- MX: The cancer couldn’t be assessed for distant metastasis and is removed from the current TNM system.
- M0: The cancer has not spread to other parts of the body.
- M1: The cancer has spread to other parts of the body.
The 5 cancer stages of the number system
TNM combinations are often given a corresponding number stage from I to IV – the Roman numerals for 1 to 4 – or sometimes a 0, which may be used by a doctor or nurse to describe the cancer to the person affected. These are less detailed designations. The criteria for the corresponding number are different for each type of cancer. For example, bladder cancer T3 N0 M0 is stage 3, whereas colon cancer T3 N0 M0 is stage 2.[^6]
Sometimes, doctors may use the letters A, B or C to divide the number stages further, such as stage 3b breast cancer.
Cancer stage 1 to 3 (stage I to III cancer)
In cancer stages 1 to 3, cancer is present. These stages vary in their features, depending on the type of cancer. In these stages, the cancer may be contained within the organ it started in or may have invaded nearby tissue or spread into regional lymph nodes. The higher the number, the larger the tumor and the more it has invaded nearby tissues.
Cancer stage 4 (stage IV)
Cancer at stage 4 has spread to distant parts of the body. This is also known as secondary, advanced or metastatic cancer.
Cancer stage 0 (Carcinoma in situ)
Stage 0 cancer, also known as carcinoma in situ (CIS), in situ neoplasm, precancerous changes, or non-invasive cancer, means that there are some abnormal cells in an area of the body, but not enough to form a tumor.
Some doctors do not consider carcinoma in situ to be cancer and do not use the term stage 0 cancer, as many cases will never develop further. These abnormal cells may not even be found, since they are often difficult to spot, except in particularly obvious places, such as in the skin, but don’t usually show up on a scan. Some exceptions include screening tests for breast cancer or cervical cancer, which can pick up carcinoma in situ.
Since this stage of cancer has not spread to nearby tissues, it is often highly curable, normally by removing all of the abnormal cells with surgery.
This type of staging is mostly used by cancer registries, but may sometimes be used by doctors and nurses to describe a cancer to the affected person. It may be applied to all types of cancer.
In situ describes abnormal cells that are only present in the layer of cells in which they developed.
This cancer is limited to the organ where it developed, without evidence that it has spread.
Such tumors have extended into adjoining organs or structures or spread to nearby lymph nodes.
Distant cancers have spread to distant parts of the body, generally via the blood and/or lymphatic systems.
Cancers may be classified as unknown if there is not enough information to know the stage.
Other factors included in the stage
Grading describes how abnormal cancer cells and tissue look under a microscope. It may provide an indicator of how quickly the cancer is likely to grow and spread.
If the tumor cells and the tissue structure are close to normal, the tumor is described as well-differentiated. Such tumors tend to grow and spread at a slower rate than those that have abnormal cells and tissue structures, which are described as poorly differentiated or undifferentiated.
Based on these cell and tissue features, a grade number can be assigned. Grading systems vary, depending on the type of cancer. Normally, the lower the number, the better the prognosis.
This is used when the grade cannot be assessed and may also be described as an undetermined grade.
The tumor cells and tissue appear close to normal and are not growing rapidly. They may be described as well differentiated or low grade.
This describes moderately differentiated tumor cells and tissue, also described as low grade.
This describes poorly differentiated or high-grade tumor cells and tissue, which may spread more quickly than normal cells.
G4 tumors may also be described as undifferentiated or high grade. These may grow or spread quickly.
Tumor markers or biomarkers and tumor genetics
These are substances found in greater amounts on the surface of cancerous cells or in the blood, urine or body tissues of some people with cancer. These help doctors to estimate the likelihood of the cancer spreading and therefore decide on a treatment plan. 
Good to know: Tumor markers are also present in some amount in people without cancer, and some non-cancerous conditions may increase the level of tumor markers found in the bodily fluids or tissues. Therefore, other tests such as biopsies will be needed to confirm a diagnosis.
Tumor markers may be measured periodically throughout treatment, as changes may indicate whether the cancer is responding to treatment. They are also used for monitoring after treatment.
Patterns of gene expression are also used as tumor markers, such as in the case of ovarian cancer and some types of leukemia.
Q: What is stage 4 cancer?
A: Cancer at stage 4 has spread from where it started to another body organ. Stage 4 cancer may also be called metastatic, advanced, secondary, or distant-spread cancer. When looked at under a microscope or tested, the metastatic cancer cells have features that resemble the primary cancer, rather than the cells where the cancer is found.
Stage 4 cancer does not always cause symptoms. As well as the symptoms of the primary cancer, some common signs of stage 4 cancer include:
- When it has spread to the bone: fractures and pain
- When it has spread to the lung: shortness of breath
- When it has spread to the liver: swelling in the stomach or yellow skin
- When it has spread to the brain: dizziness, headaches or seizures
This type of cancer is more difficult to treat. Unless the metastasis has only occurred in one specific location, localized therapies such as surgery or radiotherapy, will not cure the cancer, and alternative treatments must be used. Stage 4 cancer survival rates vary widely between types of cancer. The quality of life for each person with stage 4 cancer also varies widely.
Q: Is stage 4 cancer curable?
A: Some types of stage 4 cancer can be cured, though most cannot. However, there are treatments for all people with stage 4 cancer. The goal of these treatments may include one or more of the following:
- To stop or slow the cancer’s growth
- To relieve symptoms
- To prolong life
- Though very unlikely, to cure the cancer
Q: Cancer staging vs grading – what is the difference?
A: During diagnosis, a solid tumor will normally be given a stage and a grade. The grade is an indicator of how quickly a cancer is likely to grow and spread. The stage refers to the size or reach of a tumor and whether it has spread to other organs and tissues. For more information, see the TNM staging system, the number staging system, and grading.
Q: Can the stage change through the course of a cancer?
A: No, the stage of a cancer is not normally changed over time, even if the cancer spreads or returns. Occasionally, after a period of remission, the cancer may be restaged through tests such as imaging, biopsies, or surgery. Such cancers will be given an ‘r’ before the new stage designation.
Q: How is the stage of a cancer determined?
A: The stage of a cancer may be determined in several ways:
Clinical staging is done to all cancers when they are first diagnosed. This is based on the physical examination, imaging tests and tissue samples – known as biopsies – of affected areas.
Pathologic staging can only be determined during surgery, such as to remove a tumor or explore the extent of the cancer. This combines the result of both the clinical staging with the surgical results
Post-neoadjuvant therapy or post-therapy staging is used after systemic treatment, such as chemotherapy and/or hormone therapy, and/or radiation therapy and prior to surgery. It describes how much cancer remains.
Restaging: The stage of a cancer does not change over time, even as the cancer gets better or worse. It remains with the stage it was originally given at diagnosis. This is because survival statistics and information on treatment by stage is based on the original stage given at diagnosis. However, new information about the changes in a cancer may be added to the original stage. Occasionally, the cancer might be restaged if it returns after a period of remission.