Bone Cancer Stages

After someone is diagnosed with bone cancer, doctors will try to figure out if it has spread, and if so, how far. This process is called staging. The stage of a cancer describes how much cancer is in the body. It helps determine how serious the cancer is and how best to treat it. Doctors also use a cancer's stage when talking about survival statistics.

The information here focuses on primary bone cancers (cancers that start in bones) that most often are seen in adults. Information on Osteosarcoma, Ewing Tumors (Ewing sarcomas), and Bone Metastasis is covered separately.

The stage of a bone cancer is based on the results of physical exams, imaging tests, and any biopsies that have been done, which are described in Tests for Bone Cancer.

Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand. 

A staging system is a standard way for the cancer care team to sum up the extent of the cancer. Two main staging systems can be used to describe bone cancers. 

Musculoskeletal Tumor Society (MSTS) staging system

A system commonly used to stage bone cancer is the MSTS system, also known as the Enneking system. It is based on 3 key pieces of information:

• The grade (G) of the cancer, which is a measure of how likely it is to grow and spread, based on how it looks under the microscope. In this system, cancers are either low grade (G1) or high grade (G2). Low-grade cancer cells look more like normal cells and are less likely to grow and spread quickly, while high-grade cancer cells look more abnormal.
• The extent of the primary tumor (T), which is classified as either intracompartmental (T1), meaning it has basically remained within the bone, or extracompartmental (T2), meaning it has grown beyond the bone into other nearby structures.
• If the tumor has metastasized (M), which means it has spread to other areas, either to nearby lymph nodes (bean-sized collections of immune system cells) or other organs. Tumors that have not spread to the lymph nodes or other organs are considered M0, while those that have spread are M1.

These factors are combined to give an overall stage, using Roman numerals from I to III. Stages I and II are divided into A for intracompartmental tumors or B for extracompartmental tumors.

Stage	Grade	Tumor	Metastasis
IA	G1	T1	M0
IB	G1	T2	M0
IIA	G2	T1	M0
IIB	G2	T2	M0
III	G1 or G2	T1 orT2	M1

In summary:

• Low-grade, localized tumors are stage I.
• High-grade, localized tumors are stage II.
• Metastatic tumors (regardless of grade) are stage III.

AJCC TNM staging system

The other staging system sometimes used for bone cancer is the American Joint Committee on Cancer (AJCC) TNM system. This system is based on 4 key pieces of information:

• The extent (size) of the main (primary) tumor (T): How large is the tumor and/or has it reached nearby bones? Is it in more than one spot in the bone?
• The spread to nearby lymph nodes (N): Has the cancer spread to nearby lymph nodes?
• The spread (metastasis) to distant sites (M): Has the cancer spread to distant parts of the body, such as the lungs, other bones, or the liver?
• The grade of the cancer (G): How abnormal do the cells look under a microscope?

Numbers or letters after T, N, M, and G provide more details about each of these factors. Higher numbers generally mean the cancer has more concerning features. 

For example, the scale used for grading bone cancer in this system ranges from 1 to 3. Low-grade cancers (G1) tend to grow and spread more slowly than high-grade (G2 or G3) cancers.

• Grade 1 (G1) means the cancer looks much like normal bone tissue.
• Grade 2 (G2) means the cancer looks more abnormal.
• Grade 3 (G3) means the cancer looks very abnormal.

Once a person’s T, N, M, and G categories have been determined, this information is combined in a process called stage grouping to assign an overall stage. These stages (which are different from those of the MSTS system) are described by Roman numerals from I to IV (1 to 4), and are sometimes divided further.

Where the cancer started is another important factor in the AJCC system. In the current edition of the system (which came into use in 2018), the T categories are different for bone cancers that start in the arms, legs, trunk, skull, or facial bones, as opposed to cancers that start in the pelvis or spine. The T categories in the table below do not apply to cancers that start in the pelvis or spine. If you have a cancer that starts in one of these areas, it’s best to speak with your doctor about your cancer's stage.

Two types of stages can be assigned to bone cancers in the TNM system:

• The clinical stage is based on the results of the exams and tests that have been done before the cancer has been treated with surgery. This stage can be used to help plan treatment.
• Once surgery has been done, the pathological stage (also called the surgical stage) can be determined, based on the results of exams and imaging tests, as well as what was found during surgery.

Sometimes, the clinical and pathological stages can be different (for example, if surgery finds that the cancer has spread farther than could be seen on imaging tests). The table below describes the pathological stage of the cancer.

AJCC stage	Stage grouping	Stage description* (8 centimeters = about 3 inches)
IA	T1 N0 M0 G1 or GX	The main tumor is no more than 8 centimeters across (T1). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is low grade (G1), or the grade cannot be determined (GX).
IB	T2 N0 M0 G1 or GX	The main tumor is more than 8 centimeters across (T2). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is low grade (G1), or the grade cannot be determined (GX).
	OR
	T3 N0 M0 G1 or GX	There is more than one tumor in the same bone (T3). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is low grade (G1), or the grade cannot be determined (GX).
IIA	T1 N0 M0 G2 or G3	The main tumor is no more than 8 centimeters across (T1). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is high grade (G2 or G3).
IIB	T2 N0 M0 G2 or G3	The main tumor is more than 8 centimeters across (T2). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is high grade (G2 or G3).
III	T3 N0 M0 G2 or G3	There is more than one tumor in the same bone (T3). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0). The cancer is high grade (G2 or G3).
IVA	Any T N0 M1a Any G	The main tumor can be any size, and there may be more than one in the bone (Any T). The cancer has not spread to nearby lymph nodes (N0). It has spread only to the lungs (M1a). The cancer can be any grade (Any G).
IVB	Any T N1 Any M Any G	The main tumor can be any size, and there may be more than one in the bone (Any T). The cancer has spread to nearby lymph nodes (N1). It may or may not have spread to distant organs like the lungs or other bones (Any M). The cancer can be any grade (Any G).
	OR
	Any T Any N M1b Any G	The main tumor can be any size, and there may be more than one in the bone (Any T). The cancer might or might not have spread to nearby lymph nodes (Any N). It has spread to distant parts of the body, such as other bones, the liver, or the brain (M1b). The cancer can be any grade (Any G).

* The following additional categories are not listed on the table above:

• TX: Main tumor cannot be assessed due to lack of information.
• T0: No evidence of a primary tumor.
• NX: Regional lymph nodes cannot be assessed due to lack of information. 

For more general information on how cancers are staged, see Cancer Staging.