What Is Osteosarcoma?

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 spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

Osteosarcoma (also called osteogenic sarcoma) is the most common type of cancer that starts in the bones. The cancer cells in these tumors look like early forms of bone cells that normally help make new bone tissue, but the bone tissue in 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 develop at any age. (For information about the differences between childhood cancers and adult cancers, see Cancer in Children.)

Where does osteosarcoma start?

In children and young adults, osteosarcoma usually starts in areas where the bone is growing quickly, such as near the ends of the leg or arm 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 upper arm bone close to the shoulder (proximal humerus) is the next most common site.

Still, osteosarcoma can develop in any bone, including the bones of the pelvis (hips), shoulder, and jaw. This is especially true in older adults.

Subtypes of osteosarcoma

Based on how the cells 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 with 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
  • 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
  • Extraskeletal: a tumor that starts in a part of the body other than a bone (but still makes bone tissue)
  • Post-radiation: a tumor that starts in a bone that had once been treated with radiation

Intermediate-grade osteosarcomas

These uncommon tumors fall between high-grade and low-grade osteosarcomas. (They are usually treated the same way as 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 with a microscope.

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

The grade of the tumor plays a role in determining its stage and the type of treatment used. For more on staging, see Osteosarcoma Stages.

Other types of bone tumors

Several other types of tumors can start in the bones.

Malignant (cancerous) bone tumors

Ewing tumors are the second most common bone cancer in children. They are described in Ewing Family of Tumors.

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

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

For more information on these cancers, see Bone Cancer.

Many types of cancer that start in other organs of the body, especially cancers in adults, can spread to the bones. These are sometimes referred to as metastatic bone cancers, but they are not true bone cancers. For example, prostate cancer that spreads to the bones is still prostate cancer and is treated like prostate cancer. For more information, see Bone Metastasis.

Benign (non-cancerous) bone tumors

Not all bone tumors are cancer. Benign bone tumors do not spread to other parts of the body. They are usually not life threatening and can often be cured by surgery. There are many types of benign bone tumors, including:

  • Osteoma
  • Chondroma
  • Osteochondroma
  • Eosinophilic granuloma of bone
  • Non-ossifying fibroma
  • Enchondroma
  • Benign giant cell tumor of bone
  • Lymphangioma

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Anderson ME, Randall RL, Springfield DS, Gebhart MC. Chapter 92: Sarcomas of bone. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 5th ed. Philadelphia, Pa: Elsevier; 2014.

Gorlick R, Janeway K, Marina N. Chapter 34: Osteosarcoma. In: Pizzo PA, Poplack DG, eds. Principles and Practice of Pediatric Oncology. 7th ed. Philadelphia Pa: Lippincott Williams & Wilkins; 2016.

O’Donnell RJ, DuBois SG, Haas-Kogan DA. Chapter 91: Sarcomas of bone. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles & Practice of Oncology. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2014.

Wang LL, Gebhardt MC, Rainusso N. Osteosarcoma: Epidemiology, pathogenesis, clinical presentation, diagnosis, and histology. UpToDate. Accessed at www.uptodate.com/contents/osteosarcoma-epidemiology-pathogenesis-clinical-presentation-diagnosis-and-histology on November 28, 2017.

Last Medical Review: December 18, 2017 Last Revised: January 29, 2018

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