Staging is a process that tells the doctor how widespread a cancer may be. It will show whether the cancer has spread and how far. The treatment and prognosis (outlook) for bone cancers depend, to a large extent, on the cancer’s stage when the patient is first diagnosed.
AJCC Staging System
The American Joint Commission on Cancer (AJCC) system is used to stage all bone cancers. It combines 4 factors to determine stage that go by the initials T, N, M, and G. T stands for features of tumor (its size and if it is in more than one spot on the bone), N stands for spread to lymph nodes, M is for metastasis (spread) to distant organs, and G is for the tumor’s grade. The grade of a tumor is based on how abnormal the cells look when seen under a microscope. The higher the number, the more abnormal the cells appeared. Higher grade cancers tend to grow and spread more quickly than lower grade tumors.
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 (1-4).
T stages of bone cancer
TX: Primary tumor can’t be measured
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 is in more than one place on the same bone
N stages of bone cancer
N0: The cancer has not spread to the lymph nodes near the tumor
N1: The cancer has spread to nearby lymph nodes
M stages of bone cancer
M0: The cancer has not spread anywhere outside of the bone or nearby lymph nodes
M1: Distant metastasis (the cancer has spread)
- M1a: The cancer has spread only to the lung
- M1b: The cancer has spread to other sites (like the brain, the liver, etc.)
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 I: All stage I tumors are low grade and have not yet spread outside of the bone.
- Stage IA: T1, N0, M0, G1-G2: The tumor is 8 cm or less.
- Stage IB: T2 or T3, N0, M0, G1-G2: The tumor is either larger than 8 cm or it is in more than one place on the same bone.
Stage II: Stage II tumors have not spread outside the bone (like stage I) but are high grade.
- Stage IIA: T1, N0, M0, G3-G4: The tumor is 8 cm or less.
- Stage IIB: T2, N0, M0, G3-G4: The tumor is larger than 8 cm.
Stage III: T3, N0, M0, G3-G4: Stage III tumors have not spread outside the bone but are in more than one place on the same bone. They are high grade.
Stage IV: Stage IV tumors have spread outside of the bone they started in. They can be any grade.
- Stage IVA: Any T, N0, M1a, G1-G4: The tumor has spread to the lung.
- Stage IVB: Any T, N1, any M, G1-G4 OR Any T, any N, M1b, G1-G4: The tumor has spread to nearby lymph nodes or to distant sites other than the lung (or both).
Even though the AJCC staging system is widely accepted and used for most cancers, bone cancer specialists tend to simplify the stages into localized and metastatic. Localized includes stages I, II, and III, while metastatic is the same as stage IV.
Last Revised: 01/21/2016