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Extraskeletal Osteosarcoma

Last updated Sept. 11, 2018

Approved by: Maulik P. Purohit MD, MPH

Extraskeletal Osteosarcoma is an infrequent, but highly malignant tumor of the soft tissues, occurring in the vicinity of bones.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Adult Extraosseous Osteosarcoma
  • Adult Extraskeletal Osteosarcoma
  • Extraosseous Osteosarcoma

What is Extraskeletal Osteosarcoma? (Definition/Background Information)

  • Extraskeletal Osteosarcoma is an infrequent, but highly malignant tumor of the soft tissues, occurring in the vicinity of bones. They are primarily composed of connective tissues, bone, and cartilage material
  • Elderly adult individuals are most prone to this condition. Most of these tumors form deep within the body tissues, though a few have been found beneath the skin surface too
  • The most common location for this tumoris the thigh, followed by the buttocks, shoulder, and trunk

Who gets Extraskeletal Osteosarcoma? (Age and Sex Distribution)

  • Extraskeletal Osteosarcomas are mostly observed in the mid-to-late adult phase (40-70 years). Sometimes, young adults are also known to be affected
  • The tumor has a slight predisposition towards the male sex (male-to-female ratio 2:1)
  • There is no known ethnic/racial preference; it is known to occur worldwide

What are the Risk Factors for Extraskeletal Osteosarcoma? (Predisposing Factors)

The risk of Extraskeletal Osteosarcoma is linked to the following factors:

  • A previously performed radiotherapy for other cancer conditions. The tumor may be radiation-induced; hence, the regions that have undergone radiotherapy for other cancer conditions, have an increased risk of developing Extraskeletal Osteosarcoma
  • Certain specific genetic defects on chromosomes 8, 11, and 19, are known to increase the risk
  • The presence of a large number of chondromas (a benign tumor) occurring due to bone defects, can increase the chances of Extraskeletal Osteosarcoma. A large number of chondromas are seen in certain congenital abnormalities, such as multiple familial chondroma syndrome
  • External injury or trauma to the soft tissues can cause formation of the tumor. This may occur many, many years after the injury/trauma

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Extraskeletal Osteosarcoma? (Etiology)

  • The exact cause and mechanism of Extraskeletal Osteosarcoma formation, is unknown
  • A few medical theories have been put forward explaining the cause, one of which is:
    • Growth abnormalities in the fibrocartilaginous tissues, or in the cartilage (called epiphyseal cartilage) of long bones. During normal process, the epiphyseal cartilage is responsible for the growth of the bones
  • The tumor is thought to occur, due to some preexisting conditions and situations, which include radiation-exposure, genetic anomalies, presence of chondroma, and any well-established physical injury or trauma
  • Radiation-influenced tumor takes many years to develop, after the radiation exposure has ceased. This radiation may have been previously administered for treating any other tumor

What are the Signs and Symptoms of Extraskeletal Osteosarcoma?

The presentations are based on the location of the tumor. Extraskeletal Osteosarcoma signs and symptoms include:

  • In the initial growing phase of the tumors, they are normally asymptomatic
  • The regular locations for Extraskeletal Osteosarcoma include the thigh (almost 50% of the time), followed by the buttocks, shoulder, torso, and abdominal cavity. All tumors are observed around the bones, at these regions
  • The soft tissue tumors grow at a moderate rate, and then they suddenly start torapidly progress
  • Due to large size of the tumor, the adjoining organs, nerves, and muscles may be compressed or restricted. Often, these signs along with pain and tenderness, are the first indications of EO
  • In some individuals, organ dysfunction and internal hemorrhages may be observed. These may be sudden and spontaneous developments
  • Lesions beneath the skin (in rare cases), may appear as painful inflammations

How is Extraskeletal Osteosarcoma Diagnosed?

A diagnosis of Extraskeletal Osteosarcomais made using the following tools:

  • Physical examination, evaluation of patient’s medical history
  • Histopathological studies, conducted on a biopsy specimen
  • X-ray studies of the tumor
  • MRI scan

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Extraskeletal Osteosarcoma?

Complications of Extraskeletal Osteosarcomaare dependent on the site and severity of the tumor. These include:

  • Damage of the following organs due to metastasis - liver, bones, and lungs
  • Usually by the time Extraskeletal Osteosarcomas are detected, chances are that they would have proliferated and metastasized aggressively, damaging organs and tissues beyond repair
  • This kind of osteosarcoma is known to having a high recurrence rate, even after its surgical excision and removal
  • Deep-seated tumors (those buried inside the body tissues) may cause damage to adjoining tissues and organs
  • Blood loss during invasive treatment methods may be heavy
  • Damage to vital nerves, blood vessels, and surrounding structures, during surgery
  • Side effects from chemotherapy (such as toxicity), radiation therapy

How is Extraskeletal Osteosarcoma Treated?

Treatment measures for Extraskeletal Osteosarcoma include the following:

  • Any combination of chemotherapy, radiation therapy, and invasive procedures, may be used to treat the tumor
  • Wide surgical excision of Extraskeletal Osteosarcoma and removal of the entire lesion is the standard treatment mode. If the tumor is not fully removed, then it will recur
  • Embolization of the tumor is used to provide temporary relief from the symptoms, and reduce blood loss during a surgical procedure
  • When the tumor is at an inaccessible location, or is unsafe for surgical intervention, non-invasive procedures are adopted
  • Post-operative care is important: Minimum activity level is to be ensured until the surgical wound heals
  • Follow-up care with regular screening and check-ups are important

How can Extraskeletal Osteosarcoma be Prevented?

  • Current medical research have not established a way of preventing Extraskeletal Osteosarcoma occurrence
  • The presence of any tumor or lesion should be immediately informed to the physician and periodic follow-up screening maintained
  • Regular medical screening at periodic intervals with blood tests, scans, and physical examinations, are mandatory for those who have already endured the tumor. This is due to both its high metastasizing potential and chances of recurrence. Often several years of active vigilance is necessary

What is the Prognosis of Extraskeletal Osteosarcoma? (Outcomes/Resolutions)

  • Extraskeletal Osteosarcomas are rare, but high-malignancy cancers that have not been completely understood
  • The long-term prognosis depends on a combination of factors, such as:
    • Age of the individual
    • Tumor stage at detection
    • Size, type, and location of the tumor
    • Its Ki-67 value (a protein found in cells that is a good indicator of cell activity). A high Ki-67 index means that the tumor is growing fast
    • Tumor response to treatment and therapy, such as surgery, chemotherapy, radiation therapy
  • The long-term outcome is poor for most individuals (75% mortality over a 5-year period), given the high recurrence and metastasizing rate
  • The best treatment practice for Extraskeletal Osteosarcomas involves a combination of radiotherapy with surgical intervention. This is sometimes followed by chemotherapy (in the post-operative phase)

Additional and Relevant Useful Information for Extraskeletal Osteosarcoma:

Osteosarcoma is a class of highly cancerous, high-mortality, bone tumor. There are about 10 different types of Osteosarcoma, of which Extraskeletal Osteosarcoma is the only variant and a rare type, which occurs outside the bones.

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Dec. 16, 2013
Last updated: Sept. 11, 2018