Although people tend to regard the skeleton as a static collection of bones that, once full growth is achieved, changes very little, it is in reality one of the most active organ systems in the body. In addition to the obvious function of providing support and protection for internal organs, the skeletal system also performs a number of important chemical functions. For example, it acts as a storage and distribution center for a number of essential minerals, most notably calcium, and plays an instrumental role in the manufacture of red blood cells.
The skeleton is made up of more than 200 bones, held together by cartilage and ligaments or connective tissue. All bones are composed of the same basic elements calcium and phosphorus (mineral salts), water, and protein. The mineral salts and protein combine to form the basic structure of bone cells; the minerals are calcined to give bones their hardness. The outer sheath of the bone (the periosteum) contains blood vessels; the interior contains the spongy marrow tissue in which blood is manufactured.
Not all bones perform the same function. Some, such as the skull bones, contain very little marrow and are basically protective structures. Long bones those of the arms and legs, for example act as levers to facilitate movement. Still others, such as the flat bones of the hips and ribs, produce large quantities of red blood cells in their marrow. Like all other body tissue and organs, the bones and connective tissue may be afflicted with cancer. Most bone cancers are actually secondary tumors, meaning they arise from cancers that have metastasized or spread from other parts of the body, usually the breast, kidney, prostate, or thyroid. Cancers that actually arise in the bones and connective tissue, known medically as sarcomas, are relatively uncommon and occur mostly in young people. Each year about 2,000 primary cancers of the bone and 4,500 cancers of the connective tissue are diagnosed in the United States. This is somewhat less than one percent of all newly diagnosed cancers (excluding cancers of the skin and carcinoma in situ, such as localized cancerous changes of the cervix).
In the past, the treatment of most sarcomas involved surgery to remove or eradicate the cancerous tissue, usually with rather poor results. More
recently, however, combinations of treatments have been adopted with a greatly improved survival rate. This interdisciplinary approach usually includes conservative surgery (as opposed to the more extensive operations), radiation therapy, and anticancer chemotherapy. The use of chemotherapy, a relatively recent innovation, is probably responsible for the marked improvement in survival. Its goal is the destruction of microscopic cancers that have spread to other parts of the body from the sarcoma. These distant cancers may or may not be detected at the time of the initial diagnosis, but because of the nature of this particular type of cancer they are generally presumed to be present in most patients at the time of diagnosis of sarcoma. In addition, new chemotherapy strategies have been developed that are designed to eradicate the sarcoma itself, and these are being used with increasing frequency.