Bone Cancer

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Bone Cancer Stages

If you are diagnosed with bone cancer, your cancer care team 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.

The stage of a bone cancer is based on the results of tests such as physical exams, imaging, and biopsies.

Note: This information focuses on bone cancers that are seen most often in adults and start in the bones (primary bone cancers). Osteosarcoma, Ewing sarcoma, and bone metastases are covered separately.

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How is bone cancer staged?

A staging system is a standard way for the cancer care team to sum up the extent of a cancer. There are several staging systems used for bone cancer.

You might hear your bone cancer described using terms like:

  • Localized (one single tumor) or metastatic (tumors that have spread throughout the body)
  • Low grade or high grade

Your cancer might also be described using a numbered system:

  • The MSTS system uses numbers I (1) to III (3)
  • The AJCC system uses numbers I (1) to IV (4)

These two systems are described in greater detail below.

Musculoskeletal Tumor Society (MSTS) staging system

One system 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 is a measure of how likely it is to grow and spread. In this system, cancers are either low grade (G1) or high grade (G2), based on how the cells look under a microscope.

  • Low grade (G1): cancer cells look more like normal cells and are less likely to grow and spread quickly
  • High grade (G2): cancer cells look more abnormal

The extent of the primary tumor (T) is classified as either:

  • Intracompartmental (T1): tumor has basically remained within the bone
  • Extracompartmental (T2): tumor has grown beyond the bone into other nearby structures

If the tumor has metastasized (M), it has spread to other areas. This could be nearby lymph nodes (bean-sized collections of immune system cells) or other organs.

  • M0: tumor hasn’t spread to the lymph nodes or other organs (localized)
  • tumor has spread to lymph nodes or other organs (metastatic)

Overall stage

These factors are combined to give an overall stage, using numbers from I (1) to III (3). Stages I and II are divided into A for intracompartmental tumors or B for extracompartmental tumors.

  • Stage IA or IB: Low-grade, localized tumors
  • Stage IIA or IIB: High-grade, localized tumors
  • Stage III: Metastatic tumors, regardless of grade

AJCC TNM staging system

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

  • Size of primary tumor (T) describes the size of the main (primary) tumor and if it appears in more than one spot in the bones.
  • Lymph node spread (N) describes the extent of spread to nearby (regional) lymph nodes. Bone tumors rarely spread to the lymph nodes.
  • Metastasis (M) indicates if the cancer has metastasized (spread) to other organs of the body. The most common sites of spread are the lungs or other bones.
  • Grade (G) stands for the grade of the tumor. Under a microscope, low-grade tumor cells look more like normal cells and are less likely to grow and spread quickly. High-grade tumor cells look more abnormal.

Numbers or letters: 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.

Overall stage: Once the T, N, and M categories and the grade of the bone cancer have been determined, the information is combined into an overall stage. These stages are different from the MSTS system. They are described using numbers from I (1) to IV (4) and are sometimes divided further.

Stage IA

  • The main tumor is no more than 8 centimeters* across (T1).
  • The cancer has not spread to nearby lymph nodes (N0)
  • The cancer has not spread to distant parts of the body (M0).
  • The cancer is low grade (G1) or the grade cannot be determined (GX).

*8 centimeters = about 3 inches

Stage IB

  • The main tumor is more than 8 centimeters across (T2) or there is more than one tumor in the same bone (T3).
  • The cancer has not spread to nearby lymph nodes (N0).
  • The cancer has not spread to distant parts of the body (M0).
  • The cancer is low grade (G1) or the grade cannot be determined (GX).

Stage IIA

  • The main tumor is no more than 8 centimeters* across (T1).
  • The cancer has not spread to nearby lymph nodes (N0).
  • The cancer has not spread to distant parts of the body (M0).
  • The cancer is high grade (G2 or G3).

*8 centimeters = about 3 inches

Stage IIB

  • The main tumor is more than 8 centimeters across (T2).
  • The cancer has not spread to nearby lymph nodes (N0).
  • The cancer has not spread to distant parts of the body (M0).
  • The cancer is high grade (G2 or G3).

  • There is more than one tumor in the same bone (T3).
  • The cancer has not spread to nearby lymph nodes (N0).
  • The cancer has not spread to distant parts of the body (M0).
  • The cancer is high grade (G2 or G3).

Stage IVA  

  • 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).  
  • It can be any grade (any G). 

Stage IVB  

  • 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).  
  • It can be any grade (any G). 

OR 

  • The main tumor can be any size and there may be more than one in the bone (any T). 
  • The cancer may or may 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).  
  • It can be any grade (any G). 

Staging can be confusing and complex. If you have any questions about the stage of your cancer, ask a member of your cancer care team to explain it to you in a way you can understand.

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

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Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).

American Joint Committee on Cancer. Bone. In: AJCC Cancer Staging Manual. 8th ed. New York, NY: Springer; 2017: 471-486. 

Enneking WF. A system of staging musculoskeletal neoplasms. Clin Orthop Relat Res. 1986;(204):9-24. 

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Bone Cancer. v.1.2026 – September 11, 2025. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/bone.pdf on October 7, 2025. 

Last Revised: January 5, 2026

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.

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