Risk Factors for Cancer

1. Genetics and Family History

Some cancers are linked to inherited genetic changes passed down within families. In certain families, the risk of cancer may be higher because of:

• Inherited gene mutations
• Interactions between multiple genes
• A combination of genetics and shared environmental factors

If several family members have had cancer, the risk for other relatives may also be increased.

Abnormal genes or chromosome changes can affect how cells grow and divide. When these control mechanisms stop working properly, cells may grow uncontrollably and develop into cancer.

2. Age

The risk of cancer generally increases with age. Over time, the body is exposed to harmful factors such as:

• Pollution
• Ultraviolet (UV) radiation
• Chemicals
• Tobacco smoke

At the same time, the body’s ability to repair damaged cells and maintain immune function may gradually weaken, increasing the chance of abnormal cell growth.

Some cancers in children are linked to genetic mutations that occur before birth or are inherited from parents. However, most cancers are more common in older adults.

3. Environmental Factors and Harmful Exposures

Many environmental factors may increase cancer risk.

Tobacco and Secondhand Smoke

Tobacco smoke contains carcinogens that increase the risk of:

• Lung cancer
• Mouth and throat cancers
• Esophageal cancer
• Kidney cancer
• Bladder cancer

Pollution and Chemicals

Long-term exposure to:

• Asbestos
• Industrial waste
• Pesticides
• Toxic chemicals

May be associated with cancers such as lung cancer, lymphoma and leukemia.

Radiation and Sunlight

Excessive exposure to UV radiation from sunlight can increase the risk of skin cancer. Other forms of ionizing radiation may also damage DNA over time.

Radon gas, a naturally occurring radioactive gas found in soil has also been linked to lung cancer when trapped inside buildings.

4. Diet and Lifestyle

Daily habits can significantly affect overall health and cancer risk. Factors that may increase the risk include:

• Heavy alcohol consumption
• Smoking
• Eating large amounts of processed, smoked or charred foods
• Overweight and obesity
• Lack of physical activity

For example:

• Excessive alcohol intake is associated with liver, esophageal, head and neck cancers
• Obesity is linked to colorectal, breast, kidney and endometrial cancers

5. Viruses, Bacteria and Infections

Some infections are associated with cancer.

Examples include:

• HPV, which is linked to cervical cancer and some cancers of the mouth, throat and anus
• Hepatitis B and C viruses, which may increase the risk of liver cancer
• Helicobacter pylori, a bacteria associated with stomach ulcers and stomach cancer

Some parasites and chronic inflammatory conditions may also increase cancer risk in certain organs.

6. Medications and Medical Treatments

Certain medications and medical treatments may affect cancer risk in specific situations.

Examples include:

• Long-term hormone therapy
• Certain hormone-related medications
• Radiation therapy and chemotherapy used to treat cancer

These treatments may slightly increase the risk of developing another cancer later in life. However, they are still used when the benefits of treatment outweigh the potential risks.

7. Geography and Living Environment

Cancer rates can vary between countries and regions. These differences may be related to:

• Diet
• Lifestyle
• Environmental exposures
• Genetics
• Access to healthcare

For example, some cancers are more common in regions with high smoking rates or high consumption of processed foods.

Source: MSD Manuals. "Risk Factors for Cancer"
By Robert Peter Gale, MD, PhD, DSC(hc), Imperial College London
Available at: https://www.msdmanuals.com/home/cancer/overview-of-cancer/risk-factors-for-cancer

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