Overview

Among the numerous potentially modifiable risk factors for cancer, reductions in tobacco use, infectious agents, excess body fatness, unhealthy diet, physical inactivity, alcohol consumption, excess exposure to ultraviolet radiation, environmental pollutants, and occupational exposures can have an important impact in reducing the morbidity and mortality associated with cancer in every part of the world. Exposures to these risk factors vary substantially across and within countries and are often associated with socioeconomic status (see Social Inequalities).

Smoking is the leading preventable cause of cancer incidence and mortality globally (see Tobacco). Smoking and smokeless tobacco cause at least 17 and three cancer types, respectively, and together account for one in five cancer deaths worldwide (Figure 2.1).

Infectious agents can cause a wide range of cancer types (see Infection). They account for about 12% of new cancer cases globally, ranging from one in 25 in some countries in North America and Oceania to one in four cancer cases in many Sub-Saharan African countries. Human papillomavirus (HPV) infection alone accounts for more than one in five cancer cases in Botswana, Zambia, and Eswatini (Map 2.1), largely due to historically high infection rates and limited access to cervical cancer screening.

Excess body fatness, unhealthy diet, and physical inactivity cause multiple types of cancer (see Body Fatness, Physical Activity, and Diet). With a rising prevalence of these risk factors, the burden of cancers associated with these risk factors has been increasing in most parts of the world. Around 4% of all new cancer deaths globally are attributed to excess body fatness (Figure 2.1).

A similar proportion of new cancer cases are attributable to alcohol consumption (see Alcohol). In addition, 70-90% of all cutaneous melanoma cases globally are attributable to excessive exposure to ultraviolet radiation from the sun and indoor tanning (see Ultraviolet Radiation).

Among adults, obesity has increased up to 3-fold across World Health Organization (WHO) regions and levels of income over the past three decades.

Other notable cancer risk factors include reproductive and hormonal factors (see Reproductive and Hormonal Factors), occupational exposures to carcinogenic agents, and environmental pollutants such as air pollution (Figure 2.3), arsenic, and aflatoxin (see Environmental Pollutants and Occupational Exposures). Climate change can also increase exposure to environmental pollutants (see Climate Change and Cancer).