Osteosarcoma is a rare type of bone cancer in which malignant (cancerous) cells produce irregular bone. Although osteosarcoma can affect people of all ages, it most often occurs in children and teens who are still growing. The tumor usually develops at the ends of the long bones, specifically around the knee and in the shoulder, but can occur anywhere in the body.
Osteosarcoma is almost always treated with a combination of chemotherapy and surgical removal of the tumor. Some tumors may be treated with surgery alone. When chemotherapy is used, it is usually given both before and after surgery to help improve outcomes.
Osteosarcoma is a type of cancer in which tumor cells produce immature bone known as osteoid. Although osteosarcoma is rare, it is the most common childhood bone cancer. Approximately 1,000 new cases of osteosarcoma are diagnosed each year in the United States—about 450 of these are in children and teens.
Osteosarcoma usually affects the body's long bones near the growth plates, areas where new tissue forms as a young person grows. Most tumors occur around the knee in either the femur (thighbone) or tibia (shinbone). However, osteosarcoma can also affect other parts of the body and can even arise outside of the bones in the soft tissues, especially in older patients.
In some cases, osteosarcoma can metastasize, or spread, to other areas of the body. When osteosarcomas spread, they most often spread to the lungs.
The cause of osteosarcoma is not known, but doctors have determined a number of factors that may make someone more likely to develop the disease.
Factors that may increase your risk for developing osteosarcoma include:
- Age. It is most common between the ages of 10 and 30 and over the age of 60.
- Gender. Males are affected more often than females.
- Previous treatment with radiation therapy
- Certain bone disorders. These include:
- Paget's disease of bone
- Fibrous dysplasia
- Certain inherited cancer syndromes. These include:
- Familial retinoblastoma
- LiFraumeni syndrome
- Bone infarct. In this condition, a disruption of the blood supply to a portion of bone leads to cell death.
Pain is the most common symptom of osteosarcoma. This pain may come and go at first but, gradually, it becomes constant. Some patients may have swelling or a mass in the area of the tumor. If the tumor is located in the leg, the patient may also develop a limp.
Because osteosarcoma weakens the bone, some patients may develop pathologic bone fractures in the area of the tumor.
Rarely, symptoms may occur due to metastasis, or spreading, of the tumor to sites other than bone.
Your doctor will talk with you about your general health and medical history and ask about your symptoms. He or she will then examine the painful area, looking for:
- Tenderness over the bone
- Swelling or a mass
- Limited range of motion in the nearby joint
Imaging studies and other tests are used to help diagnose osteosarcoma.
X-rays. X-rays provide images of dense structures, such as bone, and are very helpful in diagnosing osteosarcoma. Osteosarcoma can appear in different ways on an x-ray, but typical findings include:
- Formation of new bone in a "sunburst" pattern
- The presence of a Codman triangle—an elevation of the periosteum (outer layer of bone) from the surface of the bone
- A "cumulus cloud" appearance—a white, cloud-like lesion
While many osteosarcomas appear osteoblastic (meaning that they make new bone) on x-ray, less common findings include lesions that appear osteolytic (meaning that they break down bone), or mixed osteolytic/osteoblastic. Osteoblastic lesions appear white on x-ray, while osteolytic lesions appear dark/black.
Magnetic resonance imaging (MRI) scans. These studies provide detailed views of bone marrow and other soft tissues. An MRI will help your doctor determine the extent of the tumor and look for the spread of cancer to other parts of your body.
Computerized tomography (CT) scan. These studies provide cross-sectional images that can help your doctor further evaluate the tumor. While MRIs are generally considered more helpful than CT scans in the study of osteosarcomas, a CT scan may be ordered for patients who are unable to tolerate an enclosed MRI.
Laboratory tests. Your doctor may order a number of lab tests, including a blood test called serum alkaline phosphatase. It is important to note that, although an elevated alkaline phosphatase level can point toward a diagnosis of osteosarcoma, it can occur for other reasons, as well. For example, there is a wide range of normal alkaline phosphatase levels in growing children and teenagers—a large portion of the population affected with osteosarcoma. In addition, an elevated level of alkaline phosphatase can sometimes be seen in other diseases that involve bone growth.
Despite these limitations, your doctor may order the test to get a better overall picture of your condition and because alkaline phosphatase levels in osteosarcoma are known to be related to prognosis.
Biopsy. A biopsy is needed to confirm the diagnosis of osteosarcoma. In a biopsy, a small sample of the tumor is removed and examined under a microscope. The procedure can be performed under local anesthesia with a needle or as a small open operation.
During the biopsy, your doctor will look for irregular osteoid and other characteristic features of osteosarcomas. Irregular osteoid often appears in a collection of cells that have a spindle-shaped appearance.
Grading. The tumor will be "graded" during the biopsy. In general, the higher the grade, the more aggressive the tumor is suspected to be.
Low-grade (less aggressive) tumors typically look more like normal cells than intermediate- or high-grade tumors. High-grade (more aggressive) tumors look almost nothing like the surrounding tissue and are often associated with a poorer prognosis.
Staging. Once the tumor has been identified as osteosarcoma, your doctor will use imaging studies and other tests to determine if the cancer has spread. This process is known as "staging." Identifying the stage of the tumor will help your doctor determine the most effective treatment strategy.
Doctors have identified several different subtypes of osteosarcoma, based on how the tumors look on x-ray and under the microscope. The specific osteosarcoma subtype is determined during the biopsy. It is important to know which subtype you have since each one progresses differently and responds differently to certain treatments.
Some of the more common subtypes are described below.
Conventional osteosarcomas. This is the most common subtype of osteosarcoma. Conventional osteosarcomas most often occur near the knee—at the lower end of the femur (thighbone) or upper end of the tibia (shinbone).
Conventional osteosarcomas are divided into three different types, based on their composition:
- Osteoblastic osteosarcoma (primarily composed of osteoid)
- Chondroblastic osteosarcoma (primarily composed of cartilage)
- Fibroblastic osteosarcoma (primarily composed of spindle cells)
Telangiectatic osteosarcoma. Telangiectatic osteosarcomas are vascular tumors that produce a small amount of osteoid. On x-ray, they appear as destructive lesions that can sometimes be confused with other types of tumors. When viewed with the naked eye, telengiectatic osteosarcomas have a distinctive appearance and are often described by doctors as looking like "a bag of blood."
Small cell osteosarcoma. When examined under a microscope, small cell osteosarcoma is made up of small, round blue cells. The tumors have a similar appearance to Ewing sarcoma—another type of bone cancer. To differentiate between the two cancers, your doctor will look for the production of osteoid, a characteristic of osteosarcomas.
High-grade surface osteosarcoma. These tumors arise from the surface of bone. Although there are other osteosarcomas that arise from the surface of bone (parosteal and periosteal tumors), the cells in high-grade surface osteosarcomas look more irregular.
Paget's osteosarcoma. This subtype occurs in patients with Paget's disease of bone, a chronic bone condition that occurs most often in patients over the age of 60.
Postradiation osteosarcoma. Previous exposure to radiation in the treatment of other cancers may result in postradiation osteosarcoma. This is especially true if the radiation dose was high.
Extraskeletal osteosarcoma. These tumors arise in the body's soft tissues, rather than bone. Extraskeletal osteosarcoma is more common in older adults.
Periosteal osteosarcoma. Periosteal osteosarcomas arise from the surface of bone, most often in the diaphysis, or shaft portion, of the tibia (shinbone). The tumors produce both cartilage and osteoid.
Low-grade central osteosarcoma. These tumors occur in the shaft of the body's long bones. They usually progress slowly, but can recur as more aggressive, high-grade tumors that are at greater risk for spreading.
Parosteal osteosarcoma. Parosteal osteosarcomas arise on the surface of long bones, most often presenting as a hard mass on the back of the lower femur (thighbone), behind the knee.
Treatment of osteosarcoma depends on a number of factors, including:
- The patient's age
- The patient's overall health
- The presence of other medical conditions
- The location of the tumor
- Whether the cancer has metastasized (spread)
- The specific subtype of osteosarcoma
When treating osteosarcoma, the doctor will work closely with the patient and his or her family to develop the best possible treatment plan.
Although treatment is individualized, many osteosarcomas are treated similarly with a combination of chemotherapy and surgery.
Chemotherapy is the use of drugs to treat cancer. In patients with osteosarcoma, chemotherapy is given before surgery to help shrink the tumor and prevent the spread of the cancer. It is then given again, after surgery, to target any cancer cells that may remain and lower the risk that the cancer will return.
Various drugs are used in chemotherapy treatment for osteosarcoma. The most common ones include doxorubicin (DOX), methotrexate (MTX), dactinomycin (BCD), cyclophosphamide (INN), and cisplatin (CDDP). Most patients receive two or more of these drugs at once, which is known as combination chemotherapy.
The role of chemotherapy in the treatment of parosteal and periosteal osteosarcomas is a subject of current investigation. Since many of these tumors are low- or intermediate-grade and have not invaded much of the surrounding tissue, they can often be treated with surgery alone. However, more aggressive parosteal and periosteal osteosarcomas often require chemotherapy.
Currently, surgical treatment of localized osteosarcoma most often involves limb-salvage surgery rather than amputation. In limb-salvage surgery, the doctor removes the tumor and a portion of the healthy tissue around it, while saving as much of the nearby tendons, nerves, and blood vessels as possible. The section of bone that is removed is replaced with either a bone graft (bone taken from a donor or from another part of your own body) or a prosthesis made of metal and other materials.
When the tumor is removed, it will be analyzed under a microscope to ensure complete removal and to determine the response of tissues to the preoperative chemotherapy. If it is determined that the tumor was not completely removed, another surgery may be needed to remove the rest of it. If tissue response to the preoperative chemotherapy was poor (meaning that not enough of the tumor cells were killed), your doctor may recommend different chemotherapy drugs after surgery. If tissue response to the preoperative chemotherapy was good, your doctor will usually recommend continuing the same chemotherapy regimen as before.
Radiation therapy uses high-dose x-rays to kill cancer cells and shrink tumors. Although radiation therapy is not commonly used to treat osteosarcoma, it may be recommended for certain patients.
Recovery after limb-salvage surgery requires extensive physical therapy, rehabilitation, and follow-up care. Children, especially, need to be encouraged and supported by family and friends during this time. While they continue on chemotherapy, they may have a diminished energy level and lack motivation to exercise.
Regular follow-up visits will be needed after treatment to check for complications from treatment and cancer recurrence or spread. These visits may include blood tests or imaging studies, such as x-rays or CT scans.
The patient's prognosis after treatment will depend on many factors, including:
- Overall health
- The presence of other medical conditions
- The stage and grade of the tumor
- Blood alkaline phosphatase level at the time of diagnosis
- Whether the cancer has metastasized (spread)
- The specific subtype of osteosarcoma
In most cases, however, how the tumor responds to preoperative chemotherapy is the best predictor of prognosis. At the time the tumor is removed, the doctor will examine it under a microscope to determine the amount of necrosis (how much of the tumor has died). In general, the higher the percentage of necrosis, the better the prognosis.
Treatment is successful for many patients with osteosarcoma. Because each situation is unique, however, it is best to talk to your doctor about the specific prognosis for you or your child.
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