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Staging is a process that determines how widespread the cancer may be. The stage tells the doctor if the cancer has spread and if so, how far it has spread. The most common staging system used is the Enneking Staging System. This system categorizes tumors into three categories, depending on the grade of the tumor, the extent of the primary tumor, and whether the tumor has metastasized or not.

The grade of the tumor is a determination of how likely the cells are to grow and spread, based on their appearance under the microscope. The tumor can be low grade (G1) or high grade (G2).

The extent of the primary tumor is classified as either intracompartmental (T1) or extracompartmental (T2). If it is a T1, then the original tumor has remained in place. If the tumor is a T2, then it has extended into other nearby tissues.

If the tumor has metastasized, meaning the tumor has spread to the lymph nodes or other organs such as the lungs, then it can be classified as M1. If the tumor has not spread, then it is considered to be M0.

All three factors are combined to create an overall stage. Low-grade tumors are stage I, high-grade tumors are stage II, and metastasized tumors are all stage III. The stages are subdivided into A and B categories with A being the T1 group and B being the T2 group.

In adolescents, the majority of osteosarcomas are classified into the high-grade lesion group. All patients are stage IIB or III.

Stage	Grade	Tumor	Metastasis
IA	G1	T1	M0
IB	G1	T2	M0
IIA	G2	T1	M0
IIB	G2	T2	M0
IIIA	G1 or G2	T1	M1
IIIB	G1 or G2	T2	M1