Sarcomas account for only 1 percent of adult cancers. Sarcomas are cancers that derive from the supporting structures of the body (sarc is Greek for fleshy, and sarc-oma means fleshy growth). These supporting structures, or connective tissue, include muscle, bone, cartilage, fibrous tissue, fat, nerves, and blood and lymphatic vessels. They give form, provide support, or supply nutrients to the human body and comprise the framework on which our vital organs and glands are built. For example, besides the glandular elements, the breast contains fat, muscles, ligaments, arteries, veins, and nerves that surround and support the glands and coordinate their function. Each connective tissue structure can give rise to a cancer that would be called a sarcoma, whether it occurred in the breast or another region of the body.
Physicians who treat sarcomas have divided the disease into two broad categories: those derived from bone and those derived from the soft tissues, such as fat or muscle. Osteosarcoma and Ewing’s sarcoma are the two most common bone sarcomas and affect children and adolescents more commonly than adults. Soft-tissue sarcomas occur most often in the extremities and abdomen, though they can arise virtually anywhere in the body. For example, sarcomas of the breast are well described but account for less than 1 percent of breast cancers.
Sarcomas and carcinomas have important differences other than originating from different cell types. Carcinomas typically metastasize to the lymph nodes, lungs, bones, liver, or brain. In contrast, sarcomas usually spread to fewer locations: those that originate in the abdomen metastasize mainly to other parts of the abdomen, whereas extremity sarcomas spread predominantly to the lungs. Some sarcomas may become very large and infiltrate surrounding tissues, making them difficult to remove completely. This may be apparent to the surgeon during the operation or be revealed on analysis of the specimen by the pathologist. There are more than a hundred types of sarcomas. Many of the names are long and complicated but do bear some relation to the tissue they start in. For example, liposarcomas are derived from fat cells (lipos is Greek for fat), and angiosarcomas are derived from blood or lymphatic vessels (angos is Greek for vessel).
One sarcoma merits special attention because its treatment is unique among sarcomas. It is called GIST, which stands for gastrointestinal stromal tumor. GISTs are soft-tissue sarcomas that typically grow in the abdomen, most commonly in the stomach wall. Possible symptoms include pain, bleeding into the gastrointestinal tract, and abdominal swelling. GISTs that are not small and easily removed by surgery are incurable because they often spread throughout the abdomen. Before the late 1990s, GISTs were neglected cancers, considered to be rare and known to be resistant to chemotherapy and radiation therapy. No treatments could slow their growth, and survival was very limited. This situation changed dramatically with the discovery that the drug imatinib (Gleevec) could cause tumor regression in a high percentage of GIST sufferers.
The staging of sarcomas follows the TNM system, but as important as the stage is the grade of the tumor, because high-grade sarcomas have a much greater tendency to metastasize and limit survival compared with low-grade sarcomas. The treatment of sarcomas requires the combined input of an experienced surgeon, radiation oncologist, and medical oncologist to coordinate how surgery, radiation, or chemotherapy will be applied to lead to the best outcome. Referral to a specialized sarcoma center may be recommended.
Brain tumors are a distinct category of cancer by virtue of their occurrence in a very separate and privileged region of the body called the central nervous system. This system is protected by a barrier of bones and membranes and is bathed in a compartment of clear, sterile liquid called spinal fluid. For this and other unknown reasons, tumors that begin in the brain do not spread to the rest of the body. In contrast, brain metastases represent the spread of cancer to the brain from a primary location elsewhere in the body.
Brain tumors are also unique in that the cells that give rise to most brain tumors exist only in the brain. For example, glial cells surround and support the nerve-firing cells of the brain (called neurons) and give rise to gliomas, the most common category of brain tumor. As in other cancers of other parts of the body, there are many types of brain tumors; the specific type, grade, and location of the tumor determine the treatment approach and prognosis. Surgery, radiation, and chemotherapy treatments are tailored to each case and are coordinated by a team consisting of a neurosurgeon, medical or neuro-oncologist, and radiation oncologist.
Glioblastoma multiforme is the most frequently occurring brain tumor in adults. It is usually detected after a person experiences unremitting headaches, seizures, or neurological impairment. Maximal surgical removal of the tumor is usually followed by radiation therapy to the tumor bed in combination with administration of an oral chemotherapy drug called temozolomide (Temodar). It appears that those brain tumors that do not produce a protein called MGMT respond better to Temodar than those that make the protein; MGMT protects cancer cell DNA from the damaging effects of Temodar. Tumor testing for MGMT has not been standardized and therefore is not routinely available.
One of the most exciting advances in our understanding of brain tumors was recently made when scientists discovered that brain tumor stem cells, comprising less than 1 percent of all the cells in any tumor, may be responsible for perpetuating the cancer. New therapies will undoubtedly hone in on this critical cell population and could lead to major advancements in the treatment of brain tumors.
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