Musculoskeletal tumors can be classified into three categories: benign, malignant and metastatic.
Benign tumors do not spread from their original location and, therefore, do not pose a risk to survival of the patient. They may, however, be very painful, destructive or have a tendency to come back ("recur") even after surgical removal.
Malignant tumors have the capacity to spread to other parts of the body and thus are treated with combination of surgery and chemotherapy.
Metastatic tumors are tumors that have already spread from one location to another. The most common cancers to spread to the bony skeleton are breast, kidney, lung, thyroid and prostate cancers. Treatment in this case is mostly aimed at reducing pain and improving the quality of life of the patient.

Sarcomas are malignant tumors of the musculoskeletal system. They are far less common than “carcinomas” which arise from organs, such as breast, lung and colon cancer. At most, they represent 1% of cancers.
There are many types of sarcomas. In general, bone sarcomas are more common in children and young adults and soft tissue sarcomas more common in adults and seniors. Regardless of subtype, sarcomas share some common traits. These include the pattern of growth and spread and sensitivity to certain chemotherapeutic agents. In particular, sarcomas tend to push normal structures as they grow instead of infiltrating them. This makes surgical removal feasible in most instances.
When sarcomas spread to other parts of the body, the most common location by far is the lungs. Thus most patients will undergo CT scanning of the lungs on a regular basis. If metastasis to the lungs is discovered, many patients undergo removal of the tumor from the lungs.

Lung metastasis from sarcoma.

Grade is a measure of the aggressiveness of the tumor as seen by the pathologist on microscopic examination. Sarcomas are usually graded as "low", "intermediate" or "high" with tumors that are "high" grade are the ones most likely to recur or to spread.
Staging is a measurement of the amount of tumor in the patient and is classified by one of two systems. Most Orthopedic Oncologists use the Musculoskeletal Tumor Society Staging system for bone tumors while the American Joint Committee on Cancer staging system is used for soft tissue tumors. Stages range from stage I to Stage IV, with higher stages correlating with more advanced tumors.