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Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can then spread to other areas of the body. To learn more about cancer and how it starts and spreads, see What Is Cancer?

Ewing tumors (also known as Ewing sarcomas) are a group of cancers that start in the bones or nearby soft tissues and share some common features. These tumors can develop in people of any age, but they are most common in older children and teens. For information about the differences between childhood cancers and adult cancers, see Cancer in Children.

The main types of Ewing tumors are:

• Ewing sarcoma of bone: Ewing sarcoma that starts in a bone is the most common tumor in this family. This type of tumor was first described by Dr. James Ewing in 1921, who found it was different from the more common bone tumor, osteosarcoma. Seen with a microscope, its cells looked different from osteosarcoma cells. It was also more likely to respond to radiation therapy.
• Extraosseous Ewing tumor (EOE): Extraosseous Ewing tumors start in soft tissues around bones, but they look and act very much like Ewing sarcomas in bones. They are also known as extraskeletal Ewing sarcomas.
• Peripheral primitive neuroectodermal tumor (PPNET): This rare childhood cancer also starts in bone or soft tissue and shares many features with Ewing sarcoma of bone and EOE. Peripheral PNETs that start in the chest wall are known as Askin tumors.

Researchers have found that the cells that make up Ewing sarcoma, EOE, and PPNET are very similar. They tend to have the same DNA (gene) abnormalities and share similar proteins, which are rarely found in other types of cancers. That’s why these cancers are thought to develop from the same type of cells in the body. There are slight differences among these tumors, but they're all treated the same way.

Most Ewing tumors occur in the bones. The most common sites are:

• The pelvis (hip bones)
• The chest wall (such as the ribs or shoulder blades)
• The legs, mainly in the middle of the long bones

In contrast, osteosarcoma usually occurs at the ends of the bones of the legs or arms, especially around the knees. Extraosseous Ewing tumors can occur almost anywhere.

Most Ewing tumors occur in children and teens, but they can also occur in adults. This information focuses on the Ewing family of tumors in children and teens, but most of the content here (including much of the treatment information) applies to Ewing tumors in adults as well.

Other types of bone cancers

Several other types of cancers can start in the bones.

Osteosarcomas are the most common bone cancer in children and teens. They are described in Osteosarcoma.

Most other types of bone cancers are usually found in adults and are uncommon in children. These include:

• Chondrosarcoma (cancer that develops from cartilage)
• Undifferentiated pleomorphic sarcoma (UPS) of bone, previously known as malignant fibrous histiocytoma (MFH) of bone
• Fibrosarcoma of bone
• Chordoma
• Malignant giant cell tumor of bone

For more information on these cancers, see Bone Cancer in Adults.

Many types of cancer that start in other organs of the body can spread to the bones. These are sometimes referred to as metastatic bone cancers, but they are not true bone cancers. For example, if a rhabdomyosarcoma (a cancer that starts in muscle cells) spreads to the bones, it is still rhabdomyosarcoma and is treated like rhabdomyosarcoma. For more information, see Bone Metastases.