The stage of a cancer is how much cancer there is and how far it has spread in the body. Your doctor uses exams and tests to find out the size of the cancer and where it is. Scans can also show if the cancer has spread to nearby areas and if it has spread to other parts of the body. The stage is one of the most important things to know when deciding how to treat the cancer.

Different staging systems can be used for Ewing sarcoma.

For practical purposes (including deciding on treatment choices), doctors use a simpler system. This divides Ewing tumors into two groups:

• Localized cancer. The cancer seems to be only in the tissue (like bone or muscle) where it first started. It might also be in nearby tissues, such as lymph nodes. It hasn't spread to other parts of the body based on imaging tests and bone marrow biopsies. But even if imaging tests don't show cancer in other parts of the body, it's possible that small amounts of cancer may have spread to other places. This is why chemotherapy, which can kill cells anywhere in the body, is an important part of the treatment for Ewing sarcoma.
• Metastatic cancer. The cancer has spread from where it started to other parts of the body. This might be the lungs, other bones, or bone marrow. Less often, it spreads to lymph nodes or the liver.

Ewing sarcomas of the bone can also be staged using the TNM system from the American Joint Committee on Cancer. This is the same staging system that's used for other types of bone cancers. This more detailed staging system is based on four key pieces of information:

• T notes the size of the tumor and if it's in different parts of the same bone.
• N notes if the cancer has reached nearby lymph nodes. This is rare for bone tumors.
• M notes if the cancer has spread (metastasized) to distant parts of the body.
• G is the grade of the tumor. This is a measure of how quickly the cancer is likely to grow and spread. It's based on how the cancer cells look under the microscope. The cancer cells are graded on a 1 to 3 scale. Lower grade cancers look more like normal cells. They tend to grow and spread slowly. A higher-grade cancer is more likely to grow and spread quickly if not treated. All Ewing sarcomas are high-grade tumors or considered a G3 tumor.

The T, N, M, and G values from the TNM system are used to put these cancers into stage groupings. The groupings give an overall description of your cancer. A stage grouping is listed as a Roman numeral and can have a value of I (1), II (2), III (3), or IV (4). The higher the number, the more advanced the cancer is. Letters and numbers can be used after the Roman numeral to give more details.

Below are the stage groupings of Ewing sarcoma and what they mean.

Stage I is not used for Ewing sarcoma. This is because all Ewing sarcomas are high grade (G3). Stage I is used for other kinds of bone cancer.

Stage II is divided into these two groups:

• Stage IIA. The tumor is no more than 8 cm across and is high grade. The cancer hasn't spread to nearby lymph nodes or organs in other parts of the body.
• Stage IIB. The tumor is more than 8 cm across and is high grade. The cancer hasn't spread to nearby lymph nodes or organs in other parts of the body.

Stage III means the tumor is in more than one spot in the same bone and is high grade. The cancer hasn't spread to nearby lymph nodes or organs in other parts of the body.

Stage IV is divided into these two groups:

• Stage IVA. The cancer has spread to the lungs, but not to lymph nodes or organs in other parts of the body. It can be any size or grade.
• Stage IVB is either of these:
  • The cancer has spread to nearby lymph nodes. It may or may not have spread to organs in other parts of the body. It can be any size or grade.
  • The cancer has spread to organs in other parts of the body, but not the lungs. It may or may not have spread to nearby lymph nodes. It can be any size or grade.

Once the cancer is staged, talk with your doctor about what the stage means for treatment. Ask your doctor to explain the stage of your cancer to you in a way you can understand. Ask any questions and talk about your concerns.