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'Ãªtre; an inability to express anger or resentment; marked self dislike and distrust; and most significantly, loss of an important emotional relationship.
In 1996, 10 million people developed cancer. This number is expected to rise by 50% before 2020, and to the cancer rate is expected to double in developing countries in that time. In 1984, WHO estimated 4.3 million deaths worldwide resulting from cancer, of which 2.3 million occurred in the developing regions and the remaining 2 million in developed areas.
The trend of the current American figures for cancer is not clear. According to one source, the incidence of cancer in the USA is rising steeply. According to another source, the incidence of new cancer cases fell in the USA between 1990 and 1995 by 0.7%. The long term trend is a rise; possibly, in the shorter term, there has been a fall.
Based on the long term view, in 1999, one in two American men and one in three American women will have cancer. In the 1950s, only one in four Americans were so afflicted. In the USA from 1950 to 1998, the overall incidence of cancer rose about 60 percent, with much higher increases for cancer of some organs. For non-Hodgkins lymphoma and multiple myeloma, the increase has been 200 percent. Breast cancers have increased by 60 percent. Prostate cancer has increased 200 percent. For testicular cancer in men of the ages 28 to 35, there has been a 300 percent increase since 1950. These rates are age-adjusted and so have nothing do to with aging of the population (ie the cancer rates of a group of 50 year old men in 1990, for example, are compared to the cancer rates of a group of 50 year old men in 1950.
Based on the short term view, the number and mortality of new lung cancer cases are falling, due very probably to the sharp decline in smoking in recent decades. The incidence of breast cancer is levelling off, perhaps due to more extensive screening and multiple therapies. Colon and rectal cancer incidence are falling for no known reason, although improved diet and exercise have been proposed speculatively. The trend in prostate cancer is not clear, and the rates for Hodgkin's lymphoma and cancers that plague certain ethnic groups are still rising.
Concerning Europe, the Cancer Research Campaign estimated in 1992 that there were one million new cancer patients, and 750,000 cancer deaths, each year in the EEC/EU, representing a substantial decline in rates over 30 years. The aging of the population will increase the proportion of people in the highest risk (over-65) age group, producing at least 250,000 additional cancer cases a year in the EC by the year 2020 when 20% of the EEC/EU population will be over 65. The five most common cancers in Australia are (in descending order) bowel cancer, lung cancer, breast cancer, prostate cancer and melanomas.
75% of deaths due to cancer stem from unhealthy ways of living. 35% of all cancers are related to diet, 30% to tobacco, 7% to sexual practices, 3% to alcohol, and 3% to excessive exposure to the sun.
It is well known that lack of oxygen helps the development of more malignant cell types in solid tumours. This can be related to a defective carotid body, a small organ located in the neck that senses blood oxygen levels.