Cancer, which is not a single disease but a spectrum of diseases that includes more than 100 kinds, is characterized by the unrestrained growth of cells. Cells naturally grow and multiply, but in a healthy body this growth is controlled by a complex series of regulatory mechanisms. Cancer occurs when this regulation fails and cell division goes haywire. In most cancer cases, unrestrained growth leads to the formation of tumours which spread into and often kill normal tissue. When not attended to, such a tumour (which is called malignant) ordinarily leads to death, but there can be a long delay between its onset and the appearance of obvious symptoms.
In connective tissues (such as bone, cartilage, tendon, muscle) cancers are called sarcomas; in epithelial tissues (such as skin, bladder, lung, breast) they are called carcinomas; and in cells of the blood system they are named leukaemias.
Cancer is the second leading cause of death in the industrialized world and is rapidly becoming a major disease in the Third World as well. Though the aetiology is still undetermined, certain cancers are linked to certain environmental and lifestyle factors such as carcinogenic substances in the work environment, cigarette smoking, excess exposure to the sun, alcohol, diets high in fat and low in fibre, and stress.
Speculating about the origins of cancer, many oncologists describe a cancer personality - repressed and depressed - and draw attention to the loss or bereavement which commonly precedes the onset of the disease. Lung cancer patients are most often people unable to express strong emotions. Cancer of the cervix occurs most often among women with a tendency to helplessness or a sense of hopeless frustration derived from some unresolved conflict in the preceding six months. Overall, the most important factors in the development of malignancy are: a loss of raison d'être; an inability to express anger or resentment; marked self dislike and distrust; and most significantly, loss of an important emotional relationship.