What Are the Stages of Osteosarcoma?

The stages of osteosarcoma are used to describe how far the cancer has spread in your body. The higher the stage number, the more widespread the cancer is. These stages are important when choosing the best treatments for you.

To choose your treatment, your doctor will probably decide which of the following three stages best describes your osteosarcoma:

• Localized - The cancer affects only the bone where it started and the tissues next to the bone, such as the muscle or tendon.
• Metastatic - The cancer has spread (metastasized) to other parts of the body, such as the lungs, or to other bones that are not connected to the bone where the tumor started.
• Recurrent - The tumor has come back after it was treated. The most common places for recurrent osteosarcoma to appear are the lungs and bone. When osteosarcoma comes back (recurs), this is most likely to happen 2 or 3 years after treatment ended.

TNM System

A more formal way to describe the stages of osteosarcoma is with the TNM system. This system uses three different codes to describe the size and location of the tumor, whether it has spread to the lymph nodes around the tumor, and whether it can be found in other parts of the body.

In the TNM system, “T” plus a letter or number (0 to 4) is used to describe the size and location of the tumor. The tumor stages for osteosarcoma are:

TX - The primary, or original, tumor cannot be evaluated because of incomplete information.

T0 - There is no evidence of a primary tumor.

T1 -  The tumor is 8 cm (about 3 inches) or smaller.

T2 - The tumor is larger than 8 cm.

T3 - The tumor has spread to another site or sites on the same bone.

The "N" in the TNM system stands for node. Lymph nodes are tiny organs shaped like beans that can be found throughout the body. Lymph nodes help the body fight infections. Regional lymph nodes are near the bone where the cancer started, while distant lymph nodes are in other parts of the body. Lymph node stages are:

NX - The regional lymph nodes cannot be evaluated because of incomplete information.

N0 - The cancer has not spread into the regional lymph nodes.

N1 - The cancer has spread to nearby lymph nodes.

The "M" in the TNM system is used for cancer that has spread, or metastasized, to other parts of the body. The stages for metastatic osteosarcoma are:

MX - Distant metastasis cannot be evaluated because of incomplete information.

M0 - The cancer has not spread to the lymph nodes or other parts of the body.

M1 - The cancer has spread to other parts of the body.

M1a - The cancer has spread to the lung.

M1b - The cancer has spread to distant parts of the body, other than the lung.

Tumor Grade

The tumor grade refers to the likelihood that the cancer cells will grow and spread. The doctor determines tumor grade by looking at cancer cells under a microscope. Low-grade tumors usually grow and spread more slowly than high-grade tumors. The cells in high-grade tumors do not look or act like normal cells, and these tumors tend to grow uncontrollably.

GX - Grade cannot be evaluated because of incomplete information

G1 - Low grade, cells are well differentiated (cells have the same structure and behave in the same way as normal cells)

G2 - Low grade, cells are moderately differentiated

G3 - High grade, cells are poorly differentiated

G4 - High grade, cells are not differentiated. The cells do not look like any normal looking cells.

Stages I to IV

After the T, N, and M categories of your cancer have been identified, your doctor will combine this information with information on the tumor grade to assign a stage (I to IV) to your cancer. The grade of the tumor refers to how likely the cells are to grow and spread based on how they look under the microscope. Low-grade tumors are less likely to grow and spread than high-grade tumors.

The higher the stage number, the more serious (advanced) the cancer is.

Stage IA - The cancer is found only in the bone, is smaller than 8 cm, and is low grade (T1, N0, M0, G1-G2).

Stage IB - The cancer is found only in the bone, is larger than 8 cm, and is low grade (T2, N0, M0, G1-G2).

Stage IIA -  The cancer is found only in the bone, is smaller than 8 cm, and is high grade (T1, N0, M0, G3-G4).

Stage IIB - The cancer is found only in the bone, is larger than 8 cm, and is high grade (T2, N0, M0, G3-G4).

Stage III - The cancer is found only in the bone but has spread to other places on the bone (T3, N0, M0, any G).

Stage IVA - The cancer has spread to the lung (any T, N0, M1a, any G).

Stage IVB - The cancer has spread to lymph nodes and other parts of the body, or the cancer has spread to distant parts of the body other than the lung (Any T, N1, any M; or any T, any N, M1b, any G).

Recurrent - The cancer has come back (recurred) in the original bone or another part of the body after it has been treated. This content has been reviewed and approved by Myo Thant, MD.

Another staging system used is the The Musculoskeletal Tumor Society (MSTS) staging system which was developed by Enneking at the University of Florida. This is a surgical staging system and is not used to decide medical (chemotherapy) treatment for patients with osteosarcoma.

The MSTS staging system characterizes nonmetastatic malignant bone tumors by grade (low-grade [stage I] versus high-grade [stage II]) and further subdivides these stages according to the local anatomic extent (intracompartmental [A] versus extracompartmental [B]). For bone tumors, the compartmental status is determined by whether the tumor extends through the cortex of the involved bone; the majority of high grade osteosarcoma are extracompartmental. Patients with distant metastases are categorized as stage III.