The vast majority of cancers — about 80% — are considered sporadic. This means there is no clear cause.

For some reason, certain normal genes begin to mutate or change and then begin to multiply rapidly. There are several environmental influences that may cause these gene mutations to occur. In fact, a large number of cancers are preventable because most of these factors can be controlled with healthy lifestyle choices.

Environmental causes of cancer

• Age: Cancer is most common among people over the age of 50.
• Diet: High-fat, high-cholesterol diets are proven risk factors for several types of cancer, particularly colon cancer .
• Obesity: Although no clear link has been established, research indicates obesity may be a contributing factor to some cancers.
• Cigarettes greatly increase the risk of lung cancer, even among non-smokers who inhale secondhand smoke. Other tobacco products like pipes and chewing tobacco are linked to cancers of the mouth, tongue and throat.
• Long-term exposure to chemicals like asbestos, radon and benzene.
• Harmful ultraviolet rays from the sun are directly linked to melanoma and other forms of skin cancer.
• Some viruses have been associated with increased cancer risk. These include: Hepatitis B, Hepatitis C , Human papillomaviruses (HPV) and the Epstein-Barr virus, which causes infectious mononucleosis
• Immune system diseases, like AIDS, can make one more susceptible to some cancers.

Hereditary risks

The other 20% of cancers are hereditary. This means that an abnormal gene responsible for causing cancer is passed from parent to child. This creates a greater risk for that type of cancer in all descendants of the family.

However, just because someone has a cancer-causing gene doesn't mean they will automatically get cancer. If hereditary cancer is suspected, family members should consider genetic counseling and testing to determine their risk.

Regular cancer screenings are recommended for high-risk families so that if cancer does occur, it can be diagnosed in the early stages, when it's most responsive to treatment.