Cigarette smoking was by far the leading risk factor, contributing to nearly one in five cancer cases and about a third of all cancer deaths.
Excess body weight was next, contributing to nearly eight per cent of cancer cases, followed by alcohol consumption and excessive sun exposure, each linked to about five per cent of cases.
Physical inactivity was associated with three per cent of cancer cases.
Researchers analysed 18 risk factors across 30 types of cancers. Other risk factors that contributed to cancer cases at a lesser degree include eating red and processed meat; low consumption of fruits and vegetables; and infections with Epstein-Barr virus (EBV), and human papillomavirus (HPV), according to researchers.
The findings were published this month in the journal CA: A Cancer Journal for Clinicians.
In 2019, these lifestyle factors were linked to nearly 715,000 cancer cases and about 262,000 deaths.
The findings are not exactly new, but they add to mounting research that shows many cancer cases – and as many as half the deaths – can be prevented with lifestyle changes.
“Despite considerable declines in smoking prevalence during the past few decades, the number of lung cancer deaths attributable to cigarette smoking in the United States is alarming,” said Dr Farhad Islami, senior scientific director of cancer disparity research at the American Cancer Society and lead author of the report.
The finding underscores the importance of comprehensive tobacco control policies to stop smoking, and the need to boost screening for early detection of lung cancer, when treatment could be more effective, he added.
Islami said interventions to help maintain a healthy body weight could lower the number of cases and deaths, and is particularly important among young people with early-onset cancers. Cancer cases in people under 50 have seen a sharp rise in recent years.
Despite the findings that people have more control than they think over their cancer risk, there are still many questions about who gets cancer and why.
About 10 per cent of cancers are caused by factors that were inherited or genetic.
Colon cancer, which was once a more distant cause of cancer death in both men and women, is now a leading cause of cancer death for men and women under 50.
Experts say some risk factors including obesity and a lack of physical activity could be playing a role but they still do not know what’s causing the jump in cases among younger adults.
In Hong Kong, the Cancer Registry recorded 38,462 cancer cases in 2021, the most recent year for which statistics are available. There were 5,978 cases of lung cancer, 5,899 cases of colon cancer, 5,592 of breast cancer, 3,038 of prostate cancer, 1,771 of liver cancer and 1,306 of stomach cancer. That year, 15,108 people died of cancer.
In this new ACS study, researchers used nationally representative data on cancer incidence and mortality and risk factor prevalence to estimate the proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors overall for 30 cancer types.
The study does not include non-melanoma skin cancers.
Some cancers have more of a direct link to risk factors than others, according to the study. For example, about 90 per cent of melanoma cases are linked to ultraviolet radiation, and virtually every case of cervical cancer is linked to HPV infection, which can be prevented with an HPV vaccine, according to the study.
Lung cancer tops the list, with the most number of cases associated with a modifiable risk factor – the vast majority linked to smoking, including current and former smoking habits as well as second-hand smoke.
Being overweight was associated with 11 per cent of breast cancer cases, 14 per cent of stomach cancer cases and about half of endometrial cancer cases.
“These findings show there is a continued need to increase equitable access to preventive healthcare and awareness about preventive measures,” added Dr Ahmedin Jemal, senior vice-president, surveillance and health equity science at the American Cancer Society and senior author of the study.