Osteosarcoma

Although tumors can occur in any bone, they most frequently occur in the long bones of the arms and legs near the ends where tissue grows, called growth plates. The most common sites are the femur (thighbone) above the knee, the fibula (shinbone) below the knee and the humerus (upper arm bone). 

Other significant locations are the skull, jaw and hip bones. By the time of diagnosis, 15 to 20 percent of patients have growing tumors that have spread to the lungs or other bones.

The exact cause of osteosarcoma is unknown, and it cannot be prevented because it is a random mutation or change in the cells inside the bones. The only known environmental risk factor is exposure to radiation, as in previous radiation therapy for some other type of cancer. 

About 3 to 4 percent of children with osteosarcoma carry mutations in certain genes that increase their risk for osteosarcoma. Diseases with mutations which increase the risk for osteosarcoma include: 

• Hereditary retinoblastoma. This is a form of eye cancer in children. 
• Li-Fraumeni syndrome. Children with this inherited condition are at risk for a range of cancers. The most common include sarcoma (osteosarcoma and soft tissue sarcoma), breast cancer, leukemia, brain tumor and adrenocortical carcinoma. 
• Werner syndrome. This rare inherited condition causes premature aging as well as increased risk for a range of cancers. The most common include thyroid cancer, melanoma, sarcoma (osteosarcoma and soft tissue sarcoma) and leukemia.
• Rothmund-Thomson syndrome. This is a rare condition with symptoms including a characteristic facial rash, bone defects and a higher risk to develop osteosarcoma in childhood and skin cancer later in life. 

Symptoms of osteosarcoma may appear weeks or months before it is diagnosed. 

Symptoms include:

• Pain in the affected bone that often increases with activity
• Swelling that appears in the affected area, often a few weeks after pain begins
• A lump or mass you can feel depending on the location
• Possible break of the affected bone, although this is rare

Diagnosis of Osteosarcoma

Imaging procedures are the first step in diagnosing osteosarcoma. These may include:

• X-ray. A plain radiograph of the affected area is generally the first diagnostic test. X-ray uses radiation to show bone and soft tissue and usually shows the tumor in the bone.
• Magnetic resonance imaging (MRI). Using a magnetic field instead of radiation, a MRI scan provides the most detailed images of the tumors in the bone. 
• Computed tomography (CT) scan. CT scans of the chest can create detailed cross-sectional or even three-dimensional images to determine whether the osteosarcoma has spread to the lungs.
• Radionuclide bone scanning with technetium. This is the preferred method for evaluating the entire skeleton for the presence of osteosarcoma

If imaging locates a tumor, a surgeon will take a biopsy (tissue sample) of the tumor. A pathologist (a physician who examines tissues) will then examine the cells under a microscope for signs of cancer.

Once the pathologist confirms a diagnosis of osteosarcoma, an oncologist will evaluate all of the results to stage the tumor. Staging means assessing if the osteosarcoma has spread to the lungs or other bones.