Osteosarcoma is the most common type of cancer that starts in the bone. It is most common in children and adolescents. The cells that form osteosarcoma make bone matrix, the material that makes bone strong. But the bone matrix produced by osteosarcoma cells is not as strong as the bone matrix produced by normal bone cells.
Osteosarcoma is also known as osteogenic sarcoma. Sarcoma is a type of cancer that starts in the cells of the soft tissues or bone.
Osteosarcoma usually starts near the end of the long bones that support the legs and arms. It can also start in the bones of the skull, jaw, or pelvis. Like other cancers, osteosarcomas can spread from the bone into nearby tissues, such as muscle, tendons, and fat.
Osteosarcoma is relatively rare. About 900 people will be diagnosed with osteosarcoma each year.
Bone Tissue
Bones provide shape and support for the body. They also protect some of our organs and store certain minerals. The marrow inside the bones develops and stores blood cells.
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Our bones have several different types of cells, including:
- Osteoblasts - Form bone matrix, or connective tissue and minerals that make bones strong.
- Osteoclasts - Control the amount of bone matrix formed and help bones keep their shape. Also control the amount of minerals in the blood by depositing or taking minerals out of the bone.
- Osteocytes - Carry nutrients to the bone.
We also have three types of bone tissue:
- Compact tissue - Hard, outer tissue
- Cancellous tissue - Spongelike tissue inside the bones that contains bone marrow, which makes blood cells
- Subchondral tissue - Smooth tissue at the end of bones, which is covered in cartilage, a tough, flexible tissue.
Compact and cancellous tissues that together are called the periosteum.
Our bodies have two main types of bones:
- Flat bones - Help protect the brain and organs in the chest, abdomen, and pelvis. Examples include the skull bones and breast bone (sternum).
- Long bones - Support the legs and arms and are attached to the muscles that move the legs and arms.
How Osteosarcoma Starts
Osteosarcoma develops in the osteoblast cells that cover the bone. It usually starts in ends of the long bones around the knee, where new tissue forms as children grow. However, osteosarcoma can also start in the upper leg, lower leg, upper arm bone, pelvis, shoulder, and skull.
When cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the original tumor. For example, if osteosarcoma spreads to the lungs (metastases), the cancer cells in the lungs are osteosarcoma cells. The disease is metastatic osteosarcoma, not lung cancer, and it is treated as osteosarcoma.
Types of Osteosarcoma
There are different types of osteosarcoma based on how they look when their cells are examined closely. Depending on how they look under the microscope (basically, how much they look like normal bone), osteosarcomas are classified into grades. The grade tells your doctor how likely it is that your cancer will spread to other parts of the body.
- Low grade - The tumor has few dividing cells. These tumors can often be completely removed with surgery and do not require chemotherapy.
- Intermediate grade - These tumors are categorized as periosteal, or formed from the dense membrane that wraps the bone.
- High grade - The tumor has many dividing cells and many dead cells. These tumors tend to be aggressive and are usually treated with both surgery and chemotherapy. Most osteosarcomas in children are high grade.
Osteosarcoma is also categorized as medullary (central) or peripheral (surface).
Key Statistics
According to the American Cancer Society, about 400 of the 900 new cases of osteosarcoma that are diagnosed each year in the United States occur in children and adolescents younger than 20 years. Osteosarcoma is more common in males than females and most cases occur in people between the ages of 10 and 30. However, about 10 percent of osteosarcomas occur in people over age 60.
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