Staging is a process that tells the doctor how widespread a cancer may be. It will show if the cancer has spread and how far. Staging of bone tumors usually involves some of the imaging studies described in the section on diagnosing osteosarcoma, especially the MRI, bone scan, and either a CT or x-ray of the chest. The treatment and prognosis (outlook) for osteosarcoma depend, to a large extent, on the tumor's stage when the patient is first diagnosed.

Generally speaking, doctors (especially those treating children) divide osteosarcomas into 2 stages -- localized and metastatic -- when deciding on the best course of treatment. Formal staging systems are also used.

A localized osteosarcoma affects only the bone it starts in and the tissues next to the bone, such as muscle, tendon, or fat.

A metastatic osteosarcoma has spread to other parts of the body such as the lungs or to other bones not directly connected to the bone the tumor started in. Most often the spread is to the lungs (85%), but it can also spread to other bones, the brain, or other internal organs.

Patients who already have metastases when they are first diagnosed have a worse prognosis, although some can be cured if the metastases can be removed by surgery. The cure rate for these patients improves markedly if chemotherapy is also given.

Enneking staging system

The system used most often to formally stage osteosarcoma is the Enneking system. It is based on the grade (G) of the tumor, the extent of the original (primary) tumor (T), and whether or not the tumor has metastasized (spread) to nearby lymph nodes (bean-sized collections of immune system cells that fight infections and cancers) or other organs (M).

The grade (how likely the cells are to grow and spread, based on their appearance under the microscope) is divided into low grade (G1) and high grade (G2).

The extent of the primary tumor is classified as either intracompartmental (T1), meaning it has basically remained in place, or extracompartmental (T2), meaning it has extended into other nearby structures.

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, designated in Roman numerals from I to III. Each stage is also subdivided into A for intracompartmental tumors or B for extracompartmental tumors.

In summary, low-grade tumors are stage I, high-grade tumors are stage II, and metastatic tumors (regardless of grade) are stage III.

AJCC staging system

Another system sometimes used to stage all bone cancers is the American Joint Commission on Cancer (AJCC) system. T stands for features of tumor (its size), N stands for spread to lymph nodes, M is for metastasis (spread) to distant organs, and G is for the grade of the tumor. This information about the tumor, lymph nodes, metastasis, and grade is combined in a process called stage grouping. The stage is then described in Roman numerals from I to IV (1 to 4). Sometimes the stages are subdivided using the letters A,B,and C.

T stages of bone cancer

T0: No evidence of the tumor
T1: Tumor is 8 cm (around 3 inches) or less
T2: Tumor is larger than 8 cm
T3: Tumor has "skipped" to another site or sites on the same bone

N stages of bone cancer

N0: No spread to regional (nearby) lymph nodes
N1: The cancer has spread to nearby lymph nodes

M stages of bone cancer

M0: No distant metastasis
M1: Distant metastasis (spread of the cancer to tissues or organs far away from the original bone tumor)
M1a: The cancer has spread only to the lung
M1b: The cancer has spread to other sites

Grades of bone cancer

G1-G2: Low grade
G3-G4: High grade

TNM stage grouping

After the T, N, and M stages and the grade of the bone cancer have been determined, the information is combined and expressed as an overall stage. The process of assigning a stage number is called stage grouping. To determine the grouped stage of a cancer using the AJCC system, find the stage number below that contains the T, N, and M stages, and the proper grade.

Stage IA: T1, N0, M0, G1-G2: The tumor is confined to the bone and is less than 8 cm. It is also low grade.

Stage IB: T2, N0, M0, G1-G2: The tumor is confined to the bone and is larger than 8 cm. It is also low grade.

Stage IIA: T1, N0, M0, G3-G4: The tumor is confined to the bone and is less than 8 cm. It is also high grade.

Stage IIB: T2, N0, M0, G3-G4: The tumor is confined to the bone and is larger than 8 cm. It is also high grade.

Stage III: T3, N0, M0, Any G: The tumor is confined to the bone but has "skipped" to other sites on the bone. (It can be any grade.)

Stage IVA: Any T, N0, M1a, Any G: The tumor has spread to the lung.

Stage IVB: Any T, N1, Any M, Any G: The tumor has spread to lymph nodes and distant sites, OR Any T, Any N, M1b, Any G: The tumor has spread to distant sites other than the lung.

Last Medical Review: 01/14/2009
Last Revised: 01/14/2009