November 9, 2015 -

Osteosarcoma is the most common type of cancer that develops in bone. Like the osteoblasts in normal bone, the cells that form this cancer make bone matrix. But the bone matrix of an osteosarcoma is not as strong as that of normal bones.

Most osteosarcomas occur in children and young adults. Teens are the most commonly affected age group, but osteosarcoma can occur at any age.

In children and young adults, osteosarcoma usually develops in areas where the bone is growing quickly, such as near the ends of the long bones. Most tumors develop in the bones around the knee, either in the distal femur (the lower part of the thigh bone) or the proximal tibia (the upper part of the shinbone). The proximal humerus (the part of the upper arm bone close to the shoulder) is the next most common site. However, osteosarcoma can develop in any bone, including the bones of the pelvis (hips), shoulder, and jaw. This is especially true in older adults.

Several subtypes of osteosarcoma can be identified by how they look on x-rays and under the microscope. Some of these subtypes have a better prognosis (outlook) than others.

Based on how they look under the microscope, osteosarcomas can be classified as high grade, intermediate grade, or low grade. The grade of the tumor tells doctors how likely it is that the cancer will grow and spread to other parts of the body.

High-grade osteosarcomas: These are the fastest growing types of osteosarcoma. When seen under a microscope, they do not look like normal bone and have many cells in the process of dividing into new cells. Most osteosarcomas that occur in children and teens are high grade. There are many types of high-grade osteosarcomas (although the first 3 are the most common).

  • Osteoblastic
  • Chondroblastic
  • Fibroblastic
  • Mixed
  • Small cell
  • Telangiectatic
  • High-grade surface (juxtacortical high grade)

Other high-grade osteosarcomas include:

  • Pagetoid: a tumor that develops in someone with Paget disease of the bone
  • Extra-skeletal: a tumor that starts in a part of the body other than a bone
  • Post-radiation: a tumor that starts in a bone that had once received radiation therapy

Intermediate-grade osteosarcomas: These uncommon tumors fall in between high-grade and low-grade osteosarcomas. (They are usually treated as if they are low-grade osteosarcomas.)

  • Periosteal (juxtacortical intermediate grade)

Low-grade osteosarcomas: These are the slowest growing osteosarcomas. The tumors look more like normal bone and have few dividing cells when seen under a microscope.

  • Parosteal (juxtacortical low grade)
  • Intramedullary or intraosseous well differentiated (low-grade central)

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