Ewing sarcoma is a type of tumor that forms from a certain kind of cell in bone or soft tissue.

Ewing sarcoma most often forms in the bones of the legs, arms, feet, hands, chest, pelvis, spine, or skull. Less often, it forms in the soft tissue of the trunk, arms, legs, head, neck, retroperitoneum (area in the back of the abdomen behind the tissue that lines the abdominal wall and covers most of the organs in the abdomen), or other areas.

Ewing sarcoma is most common in adolescents and young adults (teens through mid-20s).

Ewing sarcoma has also been called peripheral primitive neuroectodermal tumor, Askin tumor (Ewing sarcoma of the chest wall), extraosseous Ewing sarcoma (Ewing sarcoma in tissue other than bone), and Ewing sarcoma family of tumors.

Undifferentiated small round cell sarcoma may also form in the bone or soft tissue.

Undifferentiated small round cell sarcoma usually forms in the bones or the muscles that are attached to bones and that help the body move. There are five types of undifferentiated small round cell sarcoma that are treated like Ewing sarcoma:

• Undifferentiated small round cell sarcoma with BCOR rearrangements. This type of bone tumor usually forms in the pelvis, arms, or legs. It may spread to other parts of the body. This type of bone tumor is more common in children younger than 18 years. In this type of round cell sarcoma, the BCOR gene is joined to the CCNB3 gene or to other genes. To diagnose this small round cell sarcoma, the tumor cells are checked for these gene changes.
• Undifferentiated small round cell sarcoma with CIC::DUX4 rearrangements. This type of soft tissue tumor usually forms in the trunk, arms, or legs. It is most common in males and in young adults between 21 and 40 years of age. In this type of small round cell sarcoma, the CIC gene is joined to the DUX4 gene. To diagnose this small round cell sarcoma, the tumor cells are checked for this gene change.
• Undifferentiated small round cell sarcoma with CIC::NUTM1 rearrangements. This type of soft tissue tumor usually forms in the central nervous system, but it can also form in the trunk. It is most common in younger patients.
• Undifferentiated small round cell sarcoma with EWSR1::NFATC2 and FUS::NFATC2 rearrangements. This type of soft tissue tumor may be a benign cyst or a malignant (cancer) tumor. It usually forms in the arms and legs. The malignant tumor is more common in males and in adults.
• Undifferentiated small round cell sarcoma with EWSR1::PATZ1 fusions. This type of soft tissue tumor usually forms in the trunk and is more common in adults.

A genetic condition may increase the risk of Ewing sarcoma and other sarcomas.

Anything that increases a person's chance of getting a disease is called a risk factor. Not every child with one or more of these risk factors will develop Ewing sarcoma or other sarcomas, and they can develop in some children who don't have any known risk factors. Children with Fanconi anemia may be at increased risk for Ewing sarcoma. Talk with your child's doctor if you think your child may be at risk.

Signs and symptoms of Ewing sarcoma include swelling and pain near the tumor.

These and other signs and symptoms may be caused by Ewing sarcoma or by other conditions. Check with your child’s doctor if they have any of the following:

• A lump (which may feel soft and warm) in the arms, legs, chest, or pelvis.
• Pain and/or swelling near the lump.
• Fever for no known reason.
• A bone that breaks for no known reason.

Tests that examine the bone and soft tissue are used to diagnose and stage Ewing sarcoma.

Procedures that make pictures of the bones and soft tissues and nearby areas help diagnose Ewing sarcoma and show how far the cancer has spread. The process used to find out if cancer cells have spread within and around the bones and soft tissues or to other parts of the body is called staging.

To plan treatment, it is important to know whether the cancer has spread to other parts of the body. Tests and procedures to detect, diagnose, and stage Ewing sarcoma are usually done at the same time.

In addition to asking about your child's personal and family health history and doing a physical exam, your child's doctor may perform the following tests and procedures to diagnose or stage Ewing sarcoma:

• MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the area where the tumor formed. This procedure is also called nuclear magnetic resonance imaging (NMRI).
• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the area where the tumor formed or the chest, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
• PET-CT scan: A procedure that combines the pictures from a PET scan and a computed tomography (CT) scan. The PET and CT scans are done at the same time on the same machine. The pictures from both scans are combined to make a more detailed picture than either test would make by itself.
• Bone scan: A procedure to check if there are rapidly dividing cells, such as cancer cells, in the bone. A very small amount of radioactive material is injected into a vein and travels through the bloodstream. The radioactive material collects in the bones with cancer and is detected by a scanner.
• Bone marrow aspiration and biopsy: The removal of bone marrow and a small piece of bone by inserting a hollow needle into the hipbone. Samples are removed from both hipbones. A pathologist views the bone marrow and bone under a microscope to see if the cancer has spread.
• X-ray: An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body, such as the chest or the area where the tumor formed.
• Complete blood count (CBC): A procedure in which a sample of blood is drawn and checked for the following:
  • The number of red blood cells, white blood cells, and platelets.
  • The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
  • The portion of the blood sample made up of red blood cells.
• Blood chemistry studies: A procedure in which a blood sample is checked to measure the amounts of certain substances, such as lactate dehydrogenase (LDH), released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.

A biopsy is done to diagnose Ewing sarcoma.

Tissue samples are removed during a biopsy so they can be viewed under a microscope by a pathologist to check for signs of cancer. It is helpful if the biopsy is done at the same center where treatment will be given. The following types of biopsy are used to diagnose Ewing sarcoma:

• Incisional biopsy: For an incisional biopsy, a sample of tissue is removed through an incision in the skin.
• Needle biopsy: For this biopsy, a sample of tissue is removed using a needle.

The specialists (pathologist, radiation oncologist, and surgeon) who will treat the patient usually work together to decide the best site to place the needle or biopsy incision. The selection of the biopsy site is important. A biopsy site that is not properly selected may result in more extensive surgery to remove the tumor or a larger area that is treated with radiation therapy.

If there is a chance that the cancer has spread to nearby lymph nodes, one or more lymph nodes may be removed and checked for signs of cancer.

The following tests may be done on the tissue that is removed:

• Cytogenetic analysis: A laboratory test in which the chromosomes of cells in a sample of tissue are counted and checked for any changes, such as broken, missing, rearranged, or extra chromosomes. Changes in certain chromosomes may be a sign of cancer. Cytogenetic analysis is used to help diagnose cancer, plan treatment, or find out how well treatment is working.
• Immunohistochemistry: A laboratory test that uses antibodies to check for certain antigens (markers) in a sample of a patient’s tissue. The antibodies are usually linked to an enzyme or a fluorescent dye. After the antibodies bind to a specific antigen in the tissue sample, the enzyme or dye is activated, and the antigen can then be seen under a microscope. This type of test is used to help diagnose cancer and to help tell one type of cancer from another type of cancer.
• Flow cytometry: A laboratory test that measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of the cells, such as size, shape, and the presence of tumor (or other) markers on the cell surface. The cells from a sample of a patient's blood, bone marrow, or other tissue are stained with a fluorescent dye, placed in a fluid, and then passed one at a time through a beam of light. The test results are based on how the cells that were stained with the fluorescent dye react to the beam of light.
• Molecular test: A laboratory test to check for certain genes, proteins, or other molecules in a sample of tissue, blood, or other body fluid. A molecular test may be done with other procedures, such as biopsies, to help diagnose some types of cancer. Molecular tests check for certain gene or chromosome changes that occur in some Ewing sarcomas.
• Reverse transcription–polymerase chain reaction (RT–PCR) test: A laboratory test in which the amount of a genetic substance called mRNA made by a specific gene is measured. An enzyme called reverse transcriptase is used to convert a specific piece of RNA into a matching piece of DNA, which can be amplified (made in large numbers) by another enzyme called DNA polymerase. The amplified DNA copies help tell whether a specific mRNA is being made by a gene. RT–PCR can be used to check the activation of certain genes that may indicate the presence of cancer cells. This test may be used to look for certain changes in a gene or chromosome, which may help diagnose cancer.

Certain factors affect prognosis (chance of recovery).

The factors that affect prognosis are different before and after treatment.

Before any treatment is given, prognosis depends on:

• Where in the body the tumor started.
• Whether the tumor formed in the bone or in soft tissue.
• Whether the tumor has spread to lymph nodes or distant parts of the body.
• How large the tumor is when the tumor is diagnosed.
• Whether the LDH level in the blood is higher than normal.
• Whether the tumor has certain gene changes.
• Whether tumor DNA has been found in the blood.
• The patient's age.
• The patient's sex.
• Whether the patient has had treatment for a different cancer.
• Whether the tumor has just been diagnosed or has recurred (come back).

After treatment is given, prognosis is affected by:

• Whether the tumor was completely removed by surgery.
• Whether the tumor responded to chemotherapy or radiation therapy.

If the cancer recurs after initial treatment, prognosis depends on:

• Whether the cancer came back more than two years after the initial treatment.
• Whether the cancer came back where it first formed and in other parts of the body, or whether the cancer came back in only one site.