Cancer arises from the transformation of normal cells into tumour cells in a multi-stage process that generally progresses from a pre-cancerous lesion to a malignant tumour.
These changes are the result of the interaction between a person’s genetic factors and three categories of external agents, including:
- physical carcinogens, such as ultraviolet and ionizing radiation;
- chemical carcinogens, such as asbestos, components of tobacco smoke, alcohol, aflatoxin (a food contaminant), and arsenic (a drinking water contaminant); and
- biological carcinogens, such as infections from certain viruses, bacteria, or parasites.
Sometimes the internal state of the body and the hormones released by the body can also contribute to the occurrence of these genetic abnormalities.
Cancer is most often diagnosed in middle-aged and elderly people, but the cell changes that cause cancer start much earlier, so it’s important to protect yourself from it at any age.
The number of people getting cancer is increasing, in part because people are living longer now than in the past.
Risk factors for cancer and other non-communicable diseases include tobacco and alcohol use, unhealthy diet, lack of physical activity and air pollution.
Some chronic infections can also be risk factors for cancer, and this problem is particularly acute in low- and middle-income countries.
In 2018, approximately 13% of cancers diagnosed worldwide were associated with carcinogenic infections such as Helicobacter pylori, human papillomavirus (HPV), hepatitis B, hepatitis C, and Epstein-Barr virus.
Hepatitis B and C viruses and some types of HPV increase the risk of developing liver and cervical cancer, respectively. HIV infection increases the risk of cervical cancer sixfold and significantly increases the risk of other cancers such as Kaposi’s sarcoma.