CAUSES OF CANCER

Causes of cancer:
Estimated percentage of total cancer deathsattributable to established causes of cancer
Risk Factor Percentage
TOBACCO 30%
ADULT DIET/OBESITY 30%
SEDENTARY LIFESTYLE 05%
OCCUPATIONAL FACTORS 05%
FAMILY HISTORY OF CANCER 05%
VIRUSES/OTHER BIOLOGIC AGENTS 05%
PERINATAL FACTORS/GROWTH 05%
REPRODUCTIVE FACTORS 03%
ALCOHOL 03%
SOCIOECONOMIC STATUS 03%
ENVIRONMENTAL POLLUTION 02%
IONIZING/ULTRAVIOLET RADIATION 02%
PRESCRIPTION DRUGS/MEDICINE PROCEDURES 01%
SALT/OTHER FOOD ADDITIVES/CONTAMINANTS 01%


Tobacco


Stemming the epidemic of tobacco smoking is our most effective means for preventing cancer.An estimated 30 percent of all cancer deaths can be attributed to tobacco use. Over the past decade, scientific studies have shown that the involuntary exposure of nonsmokers to smoke from other people's tobacco products - environmental tobacco smoke - poses a health risk for nonsmokers, including increased risks of lung cancer and other diseases.

Diet and obesity
Obesity in adult life, either due to excess energy intake or reduced expenditure, is an important cause of endometrial cancer and an established cause of post menopausal breast cancer. Obesity also is associated with cancers of the colon, rectum, and kidney. Obesity can be avoided through a combination of diet modification and increased physical activity.

Evidence to date indicates that a diet that reduces cancer risk should be:
1. High in fruits and vegetables. Fruits and vegetables may have a beneficial effect in reducing risk of several types of cancer. This finding is most firmly established for cancers of the lung, stomach, esophagus, and larynx;

2. High in legumes and grains. Legumes and grains (including bread, pasta, and cereals) may help reduce the risk of cancers of the stomach and pancreas, but more definitive evidence is needed;

3. Low in red meat. Red meat consumption has been implicated in colorectal cancer;

4. Low in salt. Reduction of salt intake may reduce stomach cancer risk;

5. Low in saturated fat from animals. Animal fat has been linked to the occurrence of prostate cancer. Added fats should be of plant origin. Olive oil in particular appears to be a good choice.

Sedentary lifestyle:
Higher levels of physical activity can reduce the incidence of colorectal cancer and may help reduce cancers of the breast and prostate. Regular physical activity during childhood and adolescence may prevent excessive weight gain and delay onset of menstruation (early age at menarche is a major risk factor for breast cancer).

Occupational factors
Occupational factors are thought to cause about five percent of all fatal cancers, mostly in the lung, bladder, and bone marrow.
Because of technological advances and a continuing shift away from industrial employment. The public must continue to demand that governmental regulations be enforced to minimize occupational exposure to carcinogens.

Family history of cancer

Certain individuals have susceptibility to cancer due to genetic mutations running in families. Fortunately, the occurrence of such mutations is not common, resulting in about two percent of all fatal cancers. Preventive measures that can be taken include genetic counseling, through which couples may decide not to have children, and more frequent screening among those at high risk.
Cancer incidence also depends on genetic polymorphisms that affect the absorption, transport, metabolic activation, or detoxification of environmental carcinogens. Genetic susceptibility due to these cancer-facilitating processes could play an interactive role in the majority of cases of cancer.

Viruses and other biologic agents:
Infectious agents, overlooked as causes of human cancer only 30 years ago, are now considered to be a factor in five percent or more of all fatal cancers. Among the more significant infectious agents are human papilloma viruses (HPV) types 16 and 18, which are implicated in cancer of the uterine cervix, and hepatitis B virus (HBV), which is implicated in liver carcinoma.

Hepatitis B and C viruses are responsible for a minority of cases of liver carcinoma. The proportion of such cases is likely to decrease following the availability of anti-HBV vaccine, improved screening of blood and blood products, and more frequent use of disposable syringes and needles by injection drug users. Measures directed against HIV transmission, coupled with declining mortality from cervical cancer due to effective Pap screening programs, suggest that human papilloma virus-related cancer mortality is also likely to decline.

Perinatal growth factors :
Excess energy intake early in life is probably responsible for the positive association between height and the risk of breast cancer and possibly other cancers. Evidence is also emerging that larger birth weight is associated positively with some cancer types, notably breast cancer and possibly prostate cancer.

Reproductive factors
Among physiologic processes, reproductive factors are the most closely linked to human cancer. Early age at menarche, late age at first birth, and late age at menopause tend to increase the risk for breast cancer, while parity is associated inversely with cancers of the endometrium and ovaries.

Several other associations have been noted, but they have not been established conclusively, are of marginal importance, or are thought to be surrogates for other recognized causal factors. For example, having multiple sexual partners, an established risk factor for cancer of the cervix, reflects likelihood of exposure to sexually transmitted viruses that are carcinogenic.

Alcohol:
The use of alcoholic beverages interacts with tobacco smoking in the causation of cancers of the upper respiratory and gastrointestinal tracts. Moreover, alcohol alone is implicated in cirrhosis-mediated liver cancer and also may cause a proportion of cancer of the breast and the large bowel.

Because the epidemiologic findings here are complicated, the advice to minimize cancer risk is also complex. Most importantly, heavy alcohol consumption should be avoided. Current guidelines define moderate drinking as two or fewer drinks per day for men and no more than one drink per day for women. Women in particular should be cautious about their level of consumption since alcohol may be involved in the etiology of breast cancer. Indeed, women who are at high risk for breast cancer (e.g., because of family history) should avoid drinking alcohol. Women who are at low risk for breast cancer but high risk for cardiovascular disease (against which moderate alcohol consumption is protective) might be counseled to drink alcohol in moderation (i.e., one drink per day). Before taking that step, however, consultation with a physician is strongly encouraged.

Socioeconomic status:
Cancers of the lung, stomach, and uterine cervix, and possibly other cancers as well, are particularly common among poor and underprivileged population groups. Poverty may be thought of as an important underlying cause for these cancers, since it is associated with increased exposure to tobacco smoke, alcoholism, poor nutrition, and certain infectious agents.

Environmental pollution:
The search for carcinogenic agents from environmental pollution has been a very active area of research, yet few causal links have been firmly established. Investigations have focused on water fluoridation, chlorinated water byproducts, metabolites of organochlorine pesticides (e.g., DDT), and residential proximity to hazardous waste sites or contaminated wells.

Ecologic studies have indicated higher mortality from lung cancer in urban areas with high air pollution levels than in rural areas. On the other hand, epidemiologic studies have not documented an increased risk of lung cancer among nonsmokers living in urban rather than in rural areas but do suggest higher risks for urban smokers compared with rural smokers.

Ionizing and ultraviolet (UV) radiation:
The ultraviolet (UV) part of the sunlight spectrum is responsible for over 90 percent of skin cancers, including skin melanomas. Both prolonged sun exposure and a history of severe sunburns have been implicated in skin cancer. Experience in other countries demonstrates that both higher public awareness of the cancer risk associated with prolonged sun exposure and greater use of sunscreens can be achieved, both resulting in reduced UV exposure.
Ionizing radiation is unquestionably carcinogenic, but the risk of cancer following exposure to low levels of radiation is generally overestimated. Even among Japanese atomic bomb survivors, only one percent have died from radiation-related cancers.
Extremely low-frequency magnetic fields have been intensively studied. The collective evidence suggests that if a risk exists at all, it is small. Radio-frequency-range electromagnetic radiation, as used in cellular telephones, is being studied currently for possible brain carcinogenicity, but at present there is no empirical evidence to substantiate this claim.

Prescription drugs and medical procedures:
Several medical products and procedures can cause cancer, but when they are administered to patients suffering from serious disease, they result in exceedingly favorable benefit-to-risk ratios. The problem is more complicated when pharmaceutical agents or procedures are applied to healthy persons for preventive purposes, since the potential benefit is smaller.

Radiotherapy can cause cancer. It is also conceivable that medical diagnostic radiation is responsible for some cancer cases, although this has been documented only for intrauterine exposures in relation to childhood leukemia. It is now generally recognized that mammography conveys a negligible risk but a substantial benefit.

Several pharmaceutical agents are human carcinogens (at different sites): cancer chemotherapeutic and immunosuppressive drugs (bone marrow); menopausal estrogens (endometrium, possibly breast); anabolic steroids (liver); and phenacetin analgesics (kidney, pelvis). Other drugs with established carcinogenicity are not used anymore (e.g., DES).

Oral contraceptives, above and beyond their social benefits, prevent many more cancers of the ovary and endometrium than they cause in the liver, while their effect in causing breast cancer appears to be minimal.

Tamoxifen, a valuable drug for the treatment of breast cancer, is now being evaluated for the primary prevention of breast cancer among healthy women who are at high risk for the disease. There is considerable but not conclusive evidence, however, that tamoxifen can cause endometrial cancer.
Salt and other food additives and contaminantsAs noted above, reduction of salt intake could reduce stomach cancer risk. No other food additive or contaminant has been linked conclusively to cancer.

Salt and other food additives and contaminants:
As noted above, reduction of salt intake could reduce stomach cancer risk. No other food additive or contaminant has been linked conclusively to cancer.