How are Ewing tumors staged?
Once a Ewing tumor has been diagnosed, tests are done to determine the stage (extent of spread) of the cancer. The stage of a Ewing tumor is one of the most important factors determining a person's outlook (prognosis) and in choosing treatment.
The stage is based on results of imaging tests and biopsies of the main tumor and other tissues, which were described in the section called "How are Ewing tumors diagnosed?"
A staging system is a standard way in which the cancer care team describes the extent of the cancer. The formal (and more detailed) staging system for Ewing tumors is the American Joint Committee on Cancer (AJCC) system. It is described here to help you understand it, in case your doctor refers to it. But for practical purposes, doctors often use a simpler system, dividing Ewing tumors into localized or metastatic groups. This is described below as well.
AJCC staging system for bone cancer
The AJCC has developed staging systems for most types of cancers. The AJCC uses one system to describe all bone cancers, including Ewing tumors that start in bone. Extraosseous Ewing (EOE) tumors (Ewing tumors that don't start in bones) are staged differently. They are staged like soft-tissue sarcomas. Information about soft-tissue sarcoma staging can be found in our document called Sarcoma - Adult Soft Tissue Cancer.
The AJCC staging system for bone cancers is based on 4 key pieces of information:
- T describes the size of the main (primary) tumor and whether it appears in different areas of the bone.
- N describes the extent of spread to nearby (regional) lymph nodes (small bean-shaped collections of immune system cells). Bone tumors rarely spread to the lymph nodes.
- M indicates whether 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 from biopsy samples 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. (All Ewing tumors are considered high-grade tumors.)
Numbers or letters appear after T, N, M, and G to provide more details about each of these factors.
T categories of bone cancer
T0: There is no evidence of a main (primary) tumor
T1: The tumor is 8 cm (around 3 inches) across or less
T2: The tumor is larger than 8 cm across
T3: The tumor is in more than one site in the same bone
N categories of bone cancer
N0: There is no spread to regional (nearby) lymph nodes
N1: The cancer has spread to nearby lymph nodes
M categories of bone cancer
M0: There is no spread (metastasis) to distant organs
M1a: The cancer has spread only to the lungs
M1b: The cancer has spread to other distant sites in the body
Grades of bone cancer
GX: Grade cannot be assessed
G1-G2: Low grade
G3-G4: High grade
(All Ewing tumors are considered to be G4.)
TNM stage grouping
Once the T, N, and M categories 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. The stages are described in Roman numerals from I to IV (1-4), and are sometimes divided further.
T1, N0, M0, G1 to G2 or GX: The tumor is 8 cm across or less and is low grade (or the grade can't be assessed). The cancer has not spread to nearby lymph nodes or to distant parts of the body.
T2 or T3, N0, M0, G1 to G2 or GX: The tumor is either larger than 8 cm across (T2) or it is in more than one place in the same bone (T3). It is low grade (or the grade can't be assessed). The cancer has not spread to nearby lymph nodes or to distant parts of the body.
T1, N0, M0, G3 to G4: The tumor is 8 cm across or less and is high grade. The cancer has not spread to nearby lymph nodes or to distant parts of the body.
T2, N0, M0, G3 to G4: The tumor is larger than 8 cm across, and is high grade. The cancer has not spread to nearby lymph nodes or to distant parts of the body.
T3, N0, M0, G3 to G4: The tumor is in more than one place in the same bone. It is high grade. The cancer has not spread to nearby lymph nodes or to distant parts of the body.
Any T, N0, M1a, any G: The tumor has spread only to the lungs. It has not spread to the lymph nodes or to other distant sites. (It can be any size or grade.)
Stage IVB (if either of these applies)
Any T, N1, any M, any G: The tumor has spread to lymph nodes. It can be any size or grade, and may or may not have spread to other distant sites.
Any T, any N, M1b, any G: The tumor has spread to distant sites other than the lungs. It can be any size or grade.
*All Ewing tumors are classified as G4 (high grade), so they cannot be stage I bone cancers.
Localized vs. metastatic stages
In practice, doctors rely on a simpler system for staging Ewing tumors to determine how best to treat them. In this system, the cancers are classified as either localized or metastatic.
Localized Ewing tumors
A localized Ewing tumor is thought to be confined to the area where it started and may also include nearby tissues such as muscle or tendons. A Ewing tumor is considered localized only after all of the imaging tests (x-rays, CT or MRI scans, and PET or bone scans) and the bone marrow biopsy and aspirate do not find distant spread to other organs.
Even when imaging tests do not show that the cancer has spread to distant areas, many patients are likely to have micrometastases (very small areas of cancer spread that can't be detected with tests). This is why chemotherapy, which can reach all parts of the body, is an important part of treatment for all Ewing tumors.
Metastatic Ewing tumors
A metastatic Ewing tumor is one that has clearly spread from where it started to distant parts of the body. Most of the time, the spread is to the lungs or to other bones or the bone marrow. Less common sites of spread include the liver and lymph nodes.
About 1 in 4 patients will have obvious spread that is found by imaging tests. But as mentioned above, many other patients are likely to have small amounts of cancer spread to other parts of the body that can't be found by imaging tests.
Last Medical Review: 04/24/2012
Last Revised: 01/18/2013