Osteosarcoma Stages

After someone is diagnosed with osteosarcoma, 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 stage of an osteosarcoma is based on the results of physical exams, imaging tests, and any biopsies that have been done, which are described in Tests for Osteosarcoma.

A staging system is a standard way for the cancer care team to sum up the extent of the cancer. When trying to figure out the best course of treatment, doctors often use a simple system that divides osteosarcomas into 2 groups: localized and metastatic. Doctors can also use more formal staging systems (see below) to describe the extent of an osteosarcoma in more detail.

Osteosarcoma staging can be confusing. If you have any questions about the stage of the cancer, ask someone on your cancer care team to explain it to you in a way you understand.

Localized osteosarcoma

A localized osteosarcoma is seen only in the bone it started in and possibly the tissues next to the bone, such as muscle, tendon, or fat.

About 4 out of 5 osteosarcomas appear to be localized when they are first found. But even when imaging tests don’t show that the cancer has spread to distant areas, most patients are likely to have very small areas of cancer spread that can’t be detected with tests. This is why chemotherapy is an important part of treatment for most osteosarcomas. If it isn’t given, the cancer is more likely to come back after surgery.

Doctors further divide localized osteosarcomas into 2 groups:

  • Resectable cancers are those in which all of the visible tumor can be removed by surgery.
  • Non-resectable (or unresectable) osteosarcomas can’t be removed completely by surgery.

Metastatic osteosarcoma

A metastatic osteosarcoma has clearly spread to other parts of the body. Most often it spreads to the lungs, but it can also spread to other bones, the brain, or other organs.

About 1 out of 5 osteosarcomas has spread at the time of diagnosis. These cancers are harder to treat, but some can be cured if the metastases can be removed by surgery. The cure rate for these cancers improves markedly if chemotherapy is also given.

Musculoskeletal Tumor Society (MSTS) Staging System

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

  • The grade (G) of the tumor, which is a measure of how likely it is to grow and spread, based on how it looks under the microscope. Tumors are either low grade (G1) or high grade (G2). Low-grade tumor cells look more like normal cells and are less likely to grow and spread quickly, while high-grade tumor 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 extended beyond the bone into other nearby structures.
  • If the tumor has metastasized (M), which means it has spread 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 further divided into A for intracompartmental tumors or B for extracompartmental tumors.






















G1 or G2

T1 orT2


In summary:

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

The TNM staging system

Another system sometimes used to stage bone cancers (including osteosarcomas) is the American Joint Commission on Cancer (AJCC) TNM system. This system is based on 4 key pieces of information:

  • T describes the size of the main (primary) tumor and if it appears in different areas of the bone.
  • N describes the extent of spread to nearby (regional) lymph nodes. Bone tumors rarely spread to the lymph nodes.
  • M indicates if the cancer has metastasized (spread) to other organs of the body. (The most common sites of spread are to the lungs or other bones.)
  • G stands for the grade of the tumor, which describes how the cells look under a microscope. Low-grade tumor cells look more like normal cells and are less likely to grow and spread quickly, while high-grade tumor cells look more abnormal.

Numbers after T, N, M, and G provide more details about each of these factors.

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 (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. For more detailed information on the AJCC TNM staging system for bone cancers, see Bone Cancer Stages.


The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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National Cancer Institute. Osteosarcoma and Malignant Fibrous Histiocytoma of Bone Treatment (PDQ®)–Health Professional Version. 2017. Accessed at www.cancer.gov/types/bone/hp/osteosarcoma-treatment-pdq on December
5, 2017.

National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Bone Cancer. Version 1.2018. Accessed at www.nccn.org/professionals/physician_gls/pdf/bone.pdf on December 5, 2017.

Wang LL, Gebhardt MC, Rainusso N. Osteosarcoma: Epidemiology, pathogenesis, clinical presentation, diagnosis, and histology. UpToDate. Accessed at www.uptodate.com/contents/osteosarcoma-epidemiology-pathogenesis-clinical-presentation-diagnosis-and-histology on November 30, 2017.

Last Medical Review: December 17, 2017 Last Revised: January 30, 2018

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