Primary bone cancer occurs in children and adolescents and starts in the cells that form bone, called osteoblasts. It is different from metastatic bone cancer, or cancer that spreads to the bone from other cancerous sites. The two most common primary bone cancers in children are osteosarcoma and the family of Ewing sarcomas. Laboratory analysis of bone cancers further divides primary bone cancers into subtypes by grade. The grade of a tumor determines how fast it grows and the likelihood of spread to other parts of the body. According to the American Cancer Society, there are about 900 cases of osteosarcoma and 250 cases of Ewing sarcoma diagnosed each year in the United States.
High-Grade Osteosarcoma
Osteosarcoma usually occurs in the long bones of the leg and arm, areas where the bones are growing rapidly in children. The most common symptoms are pain and swelling. Osteosarcoma can also develop in the bones of the pelvis, shoulder and jaw. High-grade osteosarcoma is the fastest growing of the osteosarcomas and can be further divided into osteoblastic, chondroblastic, fibroblastic, mixed, small cell, telangiectic or high-grade surface types by examining the tumor cells under a microscope. A tumor that starts in a bone that has previously received radiation may also be classified as a high-grade osteosarcoma.
Intermediate-Grade Osteosarcoma
These are the most uncommon osteosarcomas and fall between high-grade and low-grade classifications. They are usually treated as a low-grade osteosarcoma. Intermediate-grade osteosarcoma is considered periosteal, or developing in the fibrous connective tissue that wraps around the bone.
Low-Grade Osteosarcomas
These tumors are very slow growing and look more like normal bone under the microscope. The types of low-grade osteosarcomas are parosteal, on the surface of the long bones; intramedullary, inside a bone; or intraosseous, inside the bone cavity.
Ewing Sarcoma
The Ewing sarcoma family of tumors, or ESFT, is the second most common bone cancer, but it can also grow in other soft tissues, such as muscle, fat or blood vessels. According to the National Cancer Institute, Ewing sarcomas grow from primitive nerve tissue in the bone or soft tissue and occur most often along the backbone, pelvis, and in the legs and arms. While it grows in bone like osteosarcoma, the cells of classic Ewing sarcoma look different under the microscope and are more sensitive to radiation.
Peripheral Primitive Neuroectodermal Tumor
This rare bone tumor is considered part of the Ewing sarcoma tumor family, and it can grow in either the bone or the soft tissue. Tumors that grow in the chest wall are called Askin tumors.
Chondrosarcoma
A chondrosarcoma is considered a bone cancer in children, although it begins in the cartilage pads at the ends of bones and lining the joints. It begins in cartilaginous tissue in the pelvis, upper leg and shoulder. If any cancerous bone cells are found in the tumor, it will be reclassified as an osteosarcoma.
