الفهرس 
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Abstract
Cancers are a large family of diseases which involve abnormal cell growth with the potential to invade or spread to other parts of the body. They form a subset of neoplasms.
The great majority of cancers, are due to environmental factors. The remaining are due to inherited genetics. Environmental, as used by cancer researchers, means any cause that is not inherited genetically, such as lifestyle, economic and behavioral factors, and not merely pollution. Common environmental factors that contribute to cancer death include tobacco (25–30%), diet and obesity (30–35%), infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), stress, lack of physical activity, and environmental pollutants.
It is nearly impossible to prove what caused a cancer in any individual, because most cancers have multiple possible causes.
Cancer prevention is defined as active measures to decrease the risk of cancer.The vast majority of cancer cases are due to environmental risk factors,. Thus, cancer is considered a largely preventable disease. Greater than 30% of cancer deaths could be prevented by avoiding risk factors including: tobacco, overweight / obesity, an insufficient diet, physical inactivity, alcohol, sexually transmitted infections, and air pollution. Also there is role of surgery,chemoprevention ,medication ,genetic councelling, screening
and vaccination in cancer prevention.
During this essay focus had been made on the following:
• Magnitude of the problem of cancer The possible etiologic causes of cancer in general How to early detect cancer.
• Screening of the general population.
Preventive measures applied for certain types of cancer.