CANCER

any of a group of related diseases characterized by uncontrolled multiplication and disorganized growth of the affected cells; it may arise in any of the body's tissues. Cancer cells infiltrate and destroy adjacent tissues, eventually gain access to the circulatory system, are transported to distant parts of the body, and ultimately destroy the host. Concomitant with their capacity for unrestrained growth, cancer cells and the tissues they constitute lose their normal appearance, as viewed through a microscope, and assume aberrant functions. Not all abnormal growths are malignant; those that are not are referred to as benign tumours. In contrast to malignant growths, benign tumours consist of an orderly growth of cells that often are identical to or very closely resemble their normal counterparts. They are not aggressive and do not invade surrounding tissues, spread to distant sites, or kill the host. Such tumours are usually surrounded by a capsule of fibrous connective tissue. Cancer was known in antiquity. Malignant tumours have been found in Egyptian and Pre-Columbian mummies, about 5,000 and 2,400 years old, respectively. They are documented in ancient medical writings, such as the Edwin Smith and Ebers papyruses, both written about 3,500 years ago. Cancer is also seen in other species, such as birds, reptiles, and fishes. The precise equivalence between cancers in higher living forms and apparently similar growths in invertebrates and plants remains to be established. Statistics of cancer incidence and mortality show striking geographic differences, varying significantly from country to country; and within countries differences of incidence and mortality occur between the sexes, various ethnic groups, and various occupations. Epidemiologic analysis of such statistics continues to provide valuable clues and insights into the myriad factors that appear to be involved in the causation of cancer. This article examines the main causes of cancer, the spread of cancer, the various types that are known today, and the methods of treatment that are being used.