Cancer is one of the leading causes of illness and death worldwide. However, current scientific evidence shows that between 30% and 50% of cancer cases could potentially be prevented by reducing exposure to modifiable risk factors and adopting healthy lifestyle habits. Primary prevention, together with vaccination and screening programmes, is the most cost-effective strategy for reducing the overall burden of cancer.

Cancer Risk Factors

Risk factors are characteristics, exposures or behaviours that increase the likelihood of developing cancer. Having one or more risk factors does not necessarily mean that a person will develop cancer, but it may increase their susceptibility to the disease.

Modifiable Risk Factors

1. Tobacco Use

Smoking remains the leading preventable cause of cancer and the main avoidable cause of cancer-related death. Tobacco smoke contains thousands of chemicals, including dozens of known carcinogens. Smoking is associated with cancers of the lung, mouth, larynx, pharynx, oesophagus, pancreas, bladder, kidney, liver, stomach, colon and rectum, cervix, and acute myeloid leukaemia, among others.

Exposure to second-hand smoke also increases the risk of cancer.

2. Alcohol Consumption

Current evidence confirms that alcohol is a Group 1 carcinogen, according to the International Agency for Research on Cancer (IARC). There is no safe level of alcohol consumption when it comes to cancer risk.

Drinking alcohol increases the risk of cancers of the mouth, pharynx, larynx, oesophagus, liver, breast, colon and rectum. The risk increases with the amount consumed, although an increased risk has also been observed with low to moderate alcohol intake.

3. Overweight and Obesity

Being overweight or obese increases the risk of at least 13 different types of cancer, including oesophageal adenocarcinoma, colorectal cancer, postmenopausal breast cancer, endometrial cancer, kidney cancer, liver cancer, pancreatic cancer, ovarian cancer, gallbladder cancer, thyroid cancer and multiple myeloma.

The underlying mechanisms include chronic inflammation, insulin resistance, hormonal changes and metabolic alterations.

4. Unhealthy Diet

Unhealthy dietary patterns are associated with an increased risk of cancer, particularly colorectal cancer. Evidence supports limiting the consumption of processed meat, red meat and ultra-processed foods, while encouraging a diet rich in fruit, vegetables, legumes, wholegrains and fibre.

In addition, obesity resulting from an unhealthy diet contributes significantly to the risk of several types of cancer.

5. Physical Inactivity

Regular physical activity reduces the risk of several cancers, particularly colon, breast and endometrial cancers. It also helps maintain a healthy weight, improves insulin sensitivity and reduces inflammation throughout the body.

6. Ultraviolet (UV) Radiation

Excessive exposure to ultraviolet (UV) radiation from the sun or artificial tanning devices is the leading cause of skin cancer, including melanoma, basal cell carcinoma and squamous cell carcinoma.

Repeated sunburn, particularly during childhood and adolescence, significantly increases the risk.

7. Environmental and Occupational Exposure to Carcinogens

Various chemical and physical agents can increase the risk of cancer, including:

  • Asbestos (mesothelioma and lung cancer)
  • Benzene (leukaemia)
  • Arsenic (skin, lung and bladder cancers)
  • Radon (lung cancer)
  • Crystalline silica, diesel exhaust emissions and certain industrial chemicals

In addition, air pollution has been classified as a human carcinogen and is an important risk factor for lung cancer.

8. Cancer-Related Infections

Infections are an important and preventable cause of cancer, especially in low- and middle-income countries. The main infectious agents include:

  • Human Papillomavirus (HPV): cervical, anal, vulval, vaginal, penile and oropharyngeal cancers. Vaccination can prevent most of these cancers.
  • Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV): hepatocellular carcinoma. HBV vaccination and HCV treatment significantly reduce the risk.
  • Helicobacter pylori: gastric adenocarcinoma and gastric MALT lymphoma.
  • Epstein-Barr Virus (EBV): nasopharyngeal cancer and certain lymphomas.
  • Human Immunodeficiency Virus (HIV): increases the risk of Kaposi sarcoma, non-Hodgkin lymphoma, cervical cancer and other cancers.

Non-Modifiable Risk Factors

1. Age

The risk of developing most cancers increases with age due to the gradual accumulation of genetic and epigenetic changes throughout life.

2. Genetic Predisposition and Family History

Approximately 5% to 10% of cancers are associated with inherited cancer syndromes caused by germline genetic mutations. Important examples include:

  • BRCA1 and BRCA2 mutations (breast, ovarian, prostate and pancreatic cancers)
  • Lynch syndrome (colorectal, endometrial and other cancers)
  • Familial adenomatous polyposis and other hereditary cancer syndromes

A family history of cancer may reflect both shared genetic factors and common environmental exposures.

3. Sex

Some cancers are linked to specific organs or hormonal factors. For example, prostate cancer affects only men, whereas ovarian cancer and most cervical cancers affect women.

In addition, differences in cancer incidence and mortality have been observed between males and females for several types of cancer.

4. Ethnicity and Social Determinants of Health

Differences observed between ethnic groups often reflect a complex interaction of genetic, environmental, cultural and behavioural factors, as well as inequalities in access to prevention, diagnosis and treatment.

5. Pre-existing Medical Conditions

Certain chronic illnesses increase the risk of cancer, including:

  • Inflammatory bowel disease (colorectal cancer)
  • Liver cirrhosis (liver cancer)
  • Congenital or acquired immunodeficiencies
  • Long-standing chronic inflammatory diseases

Esta versión utiliza ortografía y estilo británicos de forma consistente: behaviours, programme, oesophagus, leukaemia, behavioural, tumour-related terminology, second-hand smoke, etc., y tiene un nivel de lectura apropiado para pacientes sin perder rigor científico.