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 “ How are Ewing tumors diagnosed?”
A staging system is a standard way for the cancer care team to sum up the extent of the cancer. The formal (and more detailed) staging system for Ewing tumors is the American Joint Committee on Cancer (AJCC) system for bone cancer. It is described here to help you understand it, in case your doctor refers to it. But for treatment purposes, doctors often use a simpler system, dividing Ewing tumors into localized or metastatic groups. This is described below as well.
Staging can be confusing. If you have any questions about the stage of the cancer, ask someone on the health care team to explain it to you in a way you understand.
AJCC staging system for bone cancer
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 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-sized 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. 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 after T, N, M, and G 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 can’t be assessed
G1-G2: Low grade
G3-G4: High grade
(All Ewing tumors are considered G4.)
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 (T1) and is low grade (or the grade can’t be assessed). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0).
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 (N0) or to distant parts of the body (M0).
T1, N0, M0, G3 to G4: The tumor is 8 cm across or less (T1) and is high grade (G3 or G4). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0).
T2, N0, M0, G3 to G4: The tumor is larger than 8 cm across (T2) and is high grade (G3 or G4). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0).
T3, N0, M0, G3 to G4: The tumor is in more than one place in the same bone (T3). It is high grade (G3 or G4). The cancer has not spread to nearby lymph nodes (N0) or to distant parts of the body (M0).
Any T, N0, M1a, any G: The tumor has spread only to the lungs (M1a). 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 (N1). 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 (M1b). It can be any size or grade.
*All Ewing tumors are classified as G4 (high grade), so they are never stage I bone cancers.
Localized vs. metastatic stages
Doctors use 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 have reached 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 (if done) do not find it has spread to other distant areas.
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 has clearly spread from where it started to distant parts of the body. Most of the time, it spreads to the lungs or to other bones or the bone marrow. Less commonly, it spreads to the liver or 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 seen on imaging tests.
Last Medical Review: September 18, 2014 Last Revised: February 4, 2016