Masonic Cancer Center, University of Minnesota

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Bone Cancer
Osteosarcoma

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What is osteosarcoma?

The human body is made of more than 200 bones. Although bones look and feel hard, they contain living cells that can develop into cancer. Most cancers found in the bone, however, have spread (metastasized) to the bone from another part of the body (e.g., lung, breast or kidney) or arise from blood cells in the bone marrow. These are known as cancers metastatic to the bone (bone metastases). In contrast, primary bone cancer is where a cancer begins in the bone itself. Among the relatively rare primary bone cancers, osteosarcoma is the most common type. The cancerous cells of an osteosarcoma form malignant bone tumors that can weaken bone tissue and metastasize beyond the bone into other parts of the body.

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Who gets osteosarcoma and where?

Osteosarcoma is a rare tumor. Approximately 2,000 new cases of osteosarcoma are diagnosed in the United States each year, comprising less than 1 percent of all new cancer diagnoses. The vast majority of these tumors develop in the rapidly growing bones of adolescents or young adults. Osteosarcomas can also afflict elderly persons with Paget's disease, a different bone disease that can turn into an osteosarcoma. Nevertheless, osteosarcoma is most often seen in children and young adults experiencing a growth spurt. This makes sense because all cancer is caused by an error in cellular growth resulting in the uncontrolled growth of cells. During the pubertal growth spurt, a higher number of bone cells are multiplying increasing the chance that an error in the cellular growth machinery could occur at this time.

Just as osteosarcomas are more common in fast-growing adolescents, these tumors also tend to appear in fast-growing bones, namely the bones growing around the knee (i.e., distal femur and proximal tibia) and the upper arm bone close to the shoulder (i.e., proximal humerus). Tumors can also arise in the spinal column or the pelvis. Depending upon the size of the tumor, these anatomic sites can be much more difficult to operate on to completely eradicate the mass.

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What are the different types of osteosarcoma?

There are many different types of osteosarcoma that are quite different in natural history and their potential for lethal growth. By far the most common osteosarcoma is the conventional central high-grade type which accounts for 90 percent of all osteosarcomas. The "grade" is a term used to indicate the level of aggressive tumor growth and potential for metastasis, usually based upon the appearance of the tumor under microscopic analysis. Several other types of unusual high-grade osteosarcomas are the telangiectatic, small cell and secondary (associated with another pre-existing disease such as Paget's disease or prior radiation exposure). There are low-grade osteosarcomas as well. These include the surface low-grade and conventional central low-grade osteosarcomas. For the purposes of treatment and management, the multiple types of osteosarcoma can be simply divided into two groups: high grade and low grade. Most tumors arising from the central (or medullary) portion of the bone are high grade; while most tumors arising from the surface of the bone are low grade.

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What is the cause of osteosarcoma?

Osteosarcoma is not due to any previous behavioral, dietary, environmental or genetic factor in most instances. It is a random event. There is no predisposing cause or preventative measure that a patient, parent or other family member could have taken that would have had any bearing on the chances of developing an osteosarcoma. No patient or parent should believe that they somehow contributed to the risk of developing the tumor. In a few very rare cases, there is a genetic link to the disease.

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Is osteosarcoma heritable?

There are two instances in which there is a known genetic link for osteosarcoma. An eye tumor known as retinoblastoma is associated with a mutation of a gene that also is associated with osteosarcoma. In a second situation, a familial genetic disorder known as Li-Fraumeni syndrome is manifested by a susceptibility of family members to develop a variety of cancers, including osteosarcoma, breast cancer and other types of sarcomas. Because a gene mutation can be associated with osteosarcoma, any family history of cancers should be mentioned to a treating physician.

Figure 1: X-ray of lower end of femur.

Figure 1. X-ray of lower end of femur (thigh) bone as viewed from the front. The osteosarcoma is growing and forming bone tissue (arrows) on the outside of the bone.

Figure 2. Magnetic resonance image (MRI) of same bone in Figure 1

Figure 2. Magnetic resonance image (MRI) of same bone in Figure 1. The osteosarcoma is seen within the bone and growing outwards to the left side of the image.

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What are the symptoms of osteosarcoma?

There are no particular signs or symptoms that herald the onset of osteosarcoma. Although patients usually will have pain and subsequent swelling of a body part, some patients do not have pain and only notice the swelling. An injury may direct attention to a particular body part but usually the tumor precedes the injury. If the tumor has eroded enough bone to reduce its structural integrity, a fracture may occur with only a slight amount of force applied to the bone. A fracture greatly compromises treatment and therefore any patient experiencing pain in the legs with weight bearing or in the arms with lifting should notify their physician immediately so that appropriate steps can be taken to minimize the risk of a fracture. The tumor is commonly seen on X-ray which is the best screening tool for this cancer (Figure 1). A magnetic resonance imaging (MRI) scan can be used to define more clearly the extent of the tumor and its relationship to surrounding anatomic structures (Figure 2). Other tests that can be performed on newly diagnosed patients are bone scans, positron emission tomography (PET) scans, and various blood tests looking at how active the body is at making or remodeling bone tissue.

Once a tumor is suspected based upon imaging tests, a tissue sample (biopsy) is collected before embarking upon treatment plans.. The appearance of the tumor cells under the microscope can help establish a diagnosis of osteosarcoma in most cases, but other tests can help rule out other types of cancer. Other cancers may resemble osteosarcoma under the microscope, so diagnosing this tumor is greatly aided by X-ray and other imaging studies. Ideally, a team of experts in the disciplines of pathology, radiology and orthopaedic surgery is needed to make an accurate diagnosis.

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What are the treatments for osteosarcoma?

In the United States and many other developed countries, most patients are enrolled in one of several clinical trials established by national experts in osteosarcoma. Experts from nearly all major cancer centers frequently participate in cooperative groups to design, modify and implement these clinical trials. This collaboration greatly speeds up the testing of new treatment plans and improves the chances of successfully identifying effective treatments.

Conventional central high-grade osteosarcoma (and other high-grade types) is typically treated with systemic multiagent chemotherapy for several months, followed by surgical removal of the tumor and limb reconstruction or amputation, as appropriate. Chemotherapy resumes once the surgical incision has healed sufficiently and continues for many more months. The chemotherapy is given in cycles with various drugs given during each cycle. Chemotherapy can cause a patient's blood cell count to drop, but this count rebounds to an adequate level in between each cycle. The most commonly used drugs effective against osteosarcoma are adriamycin, ifosfamide, cisplatin, methotrexate, and vincristine.. The response to chemotherapy is closely observed using various tests and scans.. Frequently patients wonder why chemotherapy is given first before surgical removal of a tumor as one might think the tumor should be removed immediately. However, giving chemotherapy prior to surgery theoretically stops the growth of microscopic deposits of tumor cells elsewhere in the body that are undetectable despite the most powerful scanners. Additionally, if chemotherapy shrinks the tumor, the surgery is greatly facilitated. Clinical studies have not shown any drop in a treatment's success when chemotherapy is given prior to tumor excision.

For surface osteosarcoma (and other low-grade types), chemotherapy is generally not advisable and instead surgical excision is performed immediately along with the necessary reconstruction of the remaining extremity after bone or joint loss using various types of bone grafts, prosthetic implants, or a combination of the two. In general, radiation is not considered an effective treatment against a low- or high-grade osteosarcoma at the doses usually given to patients.

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Does removal of the tumor require an amputation?

Figure 3. X-ray of same patient in Figures 1-2 taken 6 years after reconstruction.

Figure 3. X-ray of same patient in Figures 1-2 taken 6 years after reconstruction.

Decades ago, amputations were much more commonly needed as a means of eradicating the main tumor. Presently, however, most extremities are preserved after removing the tumor and reconstructing the remaining limb. Tumor removal involves resecting the tumor along with a layer of normal tissue surrounding it (wide local excision). This prevents the open wound from being contaminated with tumor cells as the tumor is gradually taken out. To the extent possible, nerves and major blood vessels are preserved as long as doing so does not compromise complete tumor removal. The damaged joint is reconstructed with specialized artificial joint prostheses (Figure 3). Bone is reconstructed with either a structural bone graft or a prosthetic implant. Soft tissue and muscle function restoration, at times, requires tendon reattachment. Major arteries can successfully be reconstructed using either autogenous (self-originating) vein grafts or a tube made of Gortex® material. The primary goal of limb salvage surgery is to save the limb while completely removing the tumor. Of secondary concern is reconstruction to achieve normal function, though both goals are frequently achieved (Figure 4-5).

Some unusually challenging situations involve children with lower extremity tumors who have yet to go through their growth spurt. In this situation, the growing limb can either be reconstructed with an expanding type of prosthesis or the opposite limb can be shortened slightly. An unusual surgery is also available in which the tumor and knee are removed and replaced with the healthy lower ankle which then functions as a knee by rotating the ankle joint 180 degrees (Van Ness rotationplasty). The rotated foot then serves as an excellent point of attachment for a below-knee prosthetic (artificial) foot.

Figure 1: X-ray of lower end of femur.
Photograph of the same patient in Figure 1-2 taken 6 years after femur and knee joint replacement showing the ability to straighten and lift the knee (Figure 4) as well as the amount of knee flexion (Figure 5) achieved.

Figure 4-5: Photographs of the same patient in Figure 1-2 taken 6 years after femur and knee joint replacement showing the ability to straighten and lift the knee (left) as well as the amount of knee flexion (above) achieved.

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How effective are the treatments for osteosarcoma?

Approximately three-fourths of patients diagnosed with non-metastatic osteosarcoma are successfully treated, alive and completely free of cancer five years after diagnosis. A patient's response to the chemotherapy is one of the most important predictive factors of survival. This response can be assessed by using X-rays and other imaging scans, but microscopic analysis of the percentage of tumor cells killed by the chemotherapy is a much better predictor of a patient's response.

The functional outcome of treatment depends heavily upon where within the bone the tumor began and what structures were sacrificed in order to completely remove the tumor. Reconstructive surgery with limb salvage procedures will allow a gait independent of any aids, but strenuous athletic activity is discouraged. Any type of reconstruction will have a limited durability and lifespan. Device failure through loosening, breakage, infection or fracture of the bone around the implant may require additional operations during the course of a patient's lifetime.

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Summary

Osteosarcoma is a rare and challenging cancer to treat considering the many different types of this cancer and the functional consequences of partially losing a major bone or joint. Fortunately, a multidisciplinary team of physicians using the latest biological, surgical and technological tools can successfully treat the majority of patients with this cancer and preserve the majority of their limbs.

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The content on this page was originally published in the Minnesota Masonic Cancer Center Newsletter. The author is Edward Y. Cheng, M.D., Mairs Family Professor, Department of Orthopaedic Surgery, University of Minnesota. Dr. Cheng is a member of the Masonic Cancer Center.

Content development for the Bone & Soft Tissue Cancers (Sarcomas) section was supported by the Karen Wyckoff Rein in Sarcoma Fund.