Almost 4 in 10 new cancer cases globally, or about 7 million every year, are potentially avoidable, suggests a new study of data from 185 countries. 

More specifically, out of 18.7 million new cancer cases identified in 2022, 37.8% were attributable to modifiable risk factors, with smoking, infections (particularly human papillomavirus [HPV] and hepatitis), and alcohol consumption representing the top contributors. Still, the researchers observed variations across regions and sexes in how big a role each factor played in cancer risk.

The major contributors, which also include high BMI and insufficient physical activity, “are all areas where clinicians can play a direct role through counseling, vaccination, brief interventions, and referrals,” said lead author Hanna Fink, a PhD student at the World Health Organization’s International Agency for Research on Cancer (IARC) in Lyon, France.

Previous analyses have estimated that about 44% of global cancer deaths are preventable, with US-specific estimates finding that about 40% of cancer cases and almost half of all cancer-related deaths in adults are associated with modifiable risk factors. A “key difference” from earlier research “is that we include nine established cancer-causing infectious agents,” which “were often omitted from previous global comparative analyses,” Fink said. 

Brigid M. Lynch, PhD, a cancer epidemiologist at Cancer Council Victoria, in Australia, who was not involved in the research, said the prevalence of modifiable cancer risk factors changes over time. “Up-to-date estimates are really important to help governments and civil society organizations prioritize resource allocation for primary and secondary prevention efforts,” Lynch said.

The new estimates “are reliable in that the data being fed into the models are probably the best available at this time,” she added.

The study, which was published online February 3 in Nature Medicine, used data from 2022 from IARC’s online GLOBOCAN database, which provides global statistics on 36 types of cancer. In 2022, there were nearly 20 million new cancer cases and 9.7 million deaths, with a considerably higher incidence rate in men. 

In the analysis, Fink and colleagues calculated the population-attributable fractions, or the proportion of cancer cases that would be eliminated if certain modifiable risk factors were removed. The researchers looked at 30 modifiable risk factors, which included tobacco smoking, alcohol consumption, high BMI, insufficient physical activity, smokeless tobacco and areca nut use, suboptimal breastfeeding, air pollution, ultraviolet radiation, nine infectious agents, and 13 occupational exposures. The team used population exposure data from 2012 when modeling risk to account for latency between exposure and cancer development.

Excluding non-melanoma skin cancer, the researchers identified 18.7 million new cancer cases in 2022, with 37.8% overall attributable to modifiable risk factors. The preventable cancer burden was much higher for men (45.4%) than for women (29.7%).

The leading cancer contributors globally were smoking (15%), infections (10%), and alcohol consumption (3%), with lung, cervical, and stomach cancers representing nearly half of the preventable cancers.

There were large variations between regions. For instance, only a quarter of new cases among women were linked to modifiable risk factors in Northern Africa and Western Asia, compared with 38% in sub-Saharan Africa. Men in East Asia had the highest burden of preventable cancers, at 57%, which was twice that of men in Latin America and the Caribbean (28%).

Among women, infections were the leading modifiable risk factor contributing to cancer burden in 141 countries — largely in southern regions — while tobacco smoking ranked first in 38 countries. Among men, smoking was the leading modifiable risk factor across 126 countries, followed by infections in 58 countries, primarily in sub-Saharan Africa. Ultraviolet radiation ranked first for men in Australia only.

“The pattern of risk factors is very context-specific,” Fink said. “For example, infections and cervical cancer dominate in many low-income settings, whereas tobacco, alcohol and high BMI drive much of the burden in high-income countries.”

She cautioned that the new estimates were likely conservative, as the analysis was limited “to risk factors with strong causal evidence,” and excluded things like diet or hormonal factors. 

Lynch said the authors had discussed the limitations of their work comprehensively, and one of the biggest issues was that all risk factors were treated as if they were independent, when that is not always true. For instance, tobacco and alcohol may have a “synergistic effect on the risk of cancers of the upper aero-digestive tract,” Lynch said. “This limitation means that the estimates presented by region and by sex may be underestimates.”

Fink said that while the risk factors in the study were already well-known, the “level of detail can sharpen national cancer control plans, justify investment in specific interventions (for example, HPV vaccination or tobacco taxation), and help clinicians and professional societies advocate for prevention with updated, country-specific numbers.”

The two epidemiologists both emphasized the importance of high-level interventions in addition to supporting individuals in changing unhealthy behaviors. 

“Risk factors can only be altered at the population level through policy, regulation, and changes to infrastructure — as well as changes to societal norms,” said Lynch.

Fink reported no relevant financial relationships. Lynch reported receiving payment from Elsevier for editorial duties.