What is sarcoma?

Causes and Symptoms

Sarcomas are a rare, poorly understood group of human cancers. Although the incidence of sarcomas is far lower than for the more common types of human malignancy, the disease is no less devastating to afflicted individuals and their families. The term “sarcoma” comes from the Greek term for “fleshy growth” and refers to the fact that sarcomas are malignant tumors that arise in connective tissues
of the body. In the embryo, connective tissue arises from primitive cells called the mesenchyme. During embryogenesis, the mesenchymal tissues differentiate to form the many specialized connective tissues found in the body. Malignant tumors may arise in any of these connective tissue types. Cancers arising in fatty tissue are called liposarcomas,
smooth muscle tumors are
leiomyosarcomas, cancers in developing skeletal muscle are rhabdomyosarcomas, and angiosarcomas affect the blood or lymph vessels. Other types of sarcoma include fibrosarcoma, occurring in fibroblasts; synovial sarcomas of the joints; neurofibrosarcoma, a malignancy of cells surrounding the nerves; osteosarcoma in bone tissue; and chondrosarcoma in cartilage. Gastrointestinal stromal tumors (GISTs) are a rare type of stomach cancer. Ewing’s sarcoma represents a family of
childhood malignancies occurring in very primitive cells of bone tissue and is one of the most common forms of bone cancer in children, exceeded only by osteosarcomas. Finally, Kaposi’s sarcoma is a rare sarcoma caused by infection by human herpesvirus 8. While it is a rare disease in the general population, occuring primarily among Jewish men of Mediterranean origin, it represents the most common malignancy in patients with Acquired immunodeficiency syndrome (AIDS). Kaposi’s sarcoma seems to result from the expression of a viral gene that activates growth regulatory genes in infected cells.

Although there are many types of sarcomas, this group of malignancies shares many common features, including cellular characteristics, symptoms, and treatment approaches. The causes of sarcoma, however, appear to be diverse and poorly understood. Sarcomas have been linked to environmental exposure to toxic chemicals. Genetic links have been identified in families with hereditary predispositions to cancer, including Li-Fraumeni syndrome, which results from an inherited mutation in the p53
tumor suppressor gene, and neurofibromatosis
(Von Recklinghausen’s disease), which involves an inherited mutation in the tumor suppressor gene called NF1. Many sarcomas contain genetic chromosomal rearrangements called translocations involving growth control genes similar to those observed in leukemias and lymphomas, which may suggest common features in the pathways by which these malignancies arise.
For example, the Ewing’s sarcoma family of tumors (ESFT) contains a translocation between chromosomes 11 and 22, resulting in uncontrolled expression of certain oncogenes and their products, including growth factors and kinases.

Treatment and Therapy

In addition to surgery, radiation, and chemotherapy, newer treatment approaches for sarcomas attempt to attack the tumor by targeting its genetic lesions. For example, the drug Gleevec imatinib (mesylate), used in the treatment of chronic myeloid leukemia, has also shown clinical promise in the treatment of GISTs that contain a genetic translocation that activates the cancer-causing oncogene
c-KIT. A major goal of current research on sarcomas is to better understand the mechanisms by which these tumors develop in the body in order to design treatment approaches that will target these abnormal malignant cells selectively.

The discovery of certain types of translocations common to sarcomas provides both a means to screen for genetic abnormalities that may cause the disease and a potential target for treatment. For example, some of these oncogenes may be specifically inhibited by newer families of chemotherapeutic drugs. The targeting of the c-KIT oncogene by Gleevec is an example.

Bibliography

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Parker, James N., and Philip M. Parker, eds. The Official Patient’s Sourcebook on Adult Soft Tissue Sarcoma. San Diego, Calif.: Icon Health, 2002.

"Sarcoma – Adult Soft Tissue Cancer." American Cancer Society, Jan. 17, 2013.

"Soft Tissue Sarcoma." MedlinePlus, Apr. 10, 2013.