The causes of soft tissue sarcoma are not clear in most cases, but cancers in general originate when mutations in DNA are left unchecked and cause the cells to divide rapidly, according to Mayo Clinic. The accumulation of cells for a tumor has certain properties depending on the tissue that is affected.
Soft tissue sarcomas are malignant tumors that can originate in almost any soft tissue in the body, says Mayo Clinic. The type of sarcoma is dependent on the type of tissue that develops the tumor. Common sarcomas include Kaposi's sarcoma, which originates in certain connective tissue; angiosarcoma, which affects the inner lining of blood vessels; and synovial sarcoma, which affects synovial tissue in joints.
Although the causes of soft tissue sarcomas are still unknown, doctors have identified various risk factors that place patients at risk for sarcomas and other cancers, according to the American Cancer Society. Cells divide at a regular pace due to the function of certain genes that promote regulated cell division, called oncogenes; similarly, tumor suppression genes regulate cell death so that tissues do not overgrow. Any DNA mutations in these oncogenes or tumor suppression genes can cause cells to divide too quickly or die too slowly, creating overgrown tissue masses, called tumors. Many of these mutations specifically affect soft tissue, which cause sarcoma, and research is slowly learning how the mutation of these genes causes certain sarcomas to form.