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Lifestyle factors contribute to more than 40% of new cancers and cancer deaths each year, with cigarette smoking leading the culprits, according to a study from the American Cancer Society (ACS).
Based on nationally representative data for 2014, the analysis showed that potentially modifiable risk factors accounted for 42% of cancers and 45% of cancer deaths. Cigarette smoking accounted for 19% of new cancers and 28% of all cancer deaths, followed by overweight/obesity and alcohol consumption.
If anything, the numbers might underestimate the true magnitude of lifestyle factors' impact on cancer risk, Farhad Islami, MD, PhD, strategic director of Cancer Surveillance Research at the ACS, and coauthors concluded in an article published online in CA: A Cancer Journal for Clinicians.
"The impact of all established risk factors could not be quantified, and many likely modifiable risk factors are not yet firmly established as causal," the authors concluded. "Nevertheless, these findings underscore the vast potential for reducing cancer morbidity and mortality through broad and equitable implementation of known preventive measures."
The study did not break new scientific or epidemiologic ground but reinforced evidence that prevention can play a major role in reducing the national cancer burden, Islami told MedPage Today.
"This study provided contemporary information about the proportion and number of cancers attributable to these risk factors," he said. "We've looked at one source of information about risk factors for one type of cancer and another source of information for a different type of cancer. But we didn't have a comprehensive analysis of all the contemporary data, using the same methodology to make all the results comparable."
Total cancer mortality in the United States has declined by 25% since 1991. Even so, approximately 1.6 million new diagnoses of invasive cancer will occur in 2017, and 600,000 Americans will die of cancer.
Cancer specialists have long recognized causal associations between potentially modifiable risk factors and various types of cancer, Islami and co-authors noted in their introduction. Maintaining accurate estimates of the contributions of potentially modifiable cancer risk factors can inform decisions about establishing priorities for cancer prevention and control.
To perform a contemporary analysis of modifiable factors' contribution to cancer burden, the authors used published risk factor data from the International Agency for Research on Cancer and the World Cancer Research Fund/American Institute for Cancer Research. Data on cancer occurrence and mortality (limited to adults ≥30) came from the CDC National Program of Cancer Registries, the NCI Surveillance, Epidemiology, and End Results program, and the CDC National Center for Health Statistics, all for the year 2014. The investigators included 26 cancers in their analysis.
Exposure data (cigarette smoking, alcohol intake, etc.) for the analysis came from sex- and age-specific estimates derived from nationally representative surveys.
The results suggested that potentially modifiable risk factors accounted for 659,640 of 1,579,975 cancer diagnoses in 2014. Cigarette smoking had the highest population-attributable fraction (PAF), accounting for 19.0% of all cancers, including 55.5% of potentially preventable cancers in men (184,400 of 332,320) and 35% in women (114,520 of 327,240).
Excess body weight came next but remained well behind cigarette smoking with a PAF of 7.8%, followed by alcohol intake (5.6%), ultraviolet radiation (4.7%), and physical inactivity (2.9%). Excess body weight was associated with more than twice as many potentially preventable cancers in women as in men, whether represented by PAF (10.9% versus 4.8%) or actual case volume (85,680 versus 37,670). A similar sex disparity was observed for physical activity, which accounted for 4.4% of preventable cancers in women versus 1.5% in men.
Some recent studies suggested increasing importance of excess body weight as a cancer risk factor, including speculation that obesity might overtake smoking as the leading preventable cause of cancer. The ACS analysis did not add to the support.
"Tobacco use is the far more important cancer risk factor and contributor to cancer death," said Islami. "One thing to consider is that excess body weight and obesity is very closely correlated with poor diet, physical inactivity, and alcohol consumption. We analyzed these four factors together and separately, and tobacco use still was more important."
With regard to specific types of cancer, the proportion of cases attributable to potentially modifiable risk factors exceeded 15% for 15 of the 26 cancers. The proportion ranged from 100% for cervical cancer and Kaposi sarcoma to 4.3% for ovarian cancer. Other cancers for which preventable factors accounted for at least three-fourths of total case volume included cutaneous melanoma (95.1%), anal cancer (88.2%), lung cancer (85.8%), laryngeal cancer (83.2%), and oropharyngeal/nasal cavity/paranasal sinus cancers (77.9%).
Lung cancer had the highest number of cases attributable to potentially preventable factors in men (99,860 cases) and women (85,050). For men, melanoma came next (45,120 cases), followed by colorectal cancer (43,080), and bladder cancer (28,050). Among women, the leaders in terms of number of cases of preventable cancers were breast (68,390), uterine (37,640), and colorectal (33,980).
With respect to cancer mortality, smoking accounted for almost 30% (169,180) of all cancer deaths and more than half of cancer deaths attributable to potentially modifiable risk factors (265,150). Excess body weight accounted for 6.5% of all cancer deaths.
The authors disclosed no relevant relationships with industry.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner