More than 4 in 10 Cancers and Cancer Deaths Linked to Modifiable Risk Factors

About 42% of cancer cases and 45% of cancer deaths in the United States are linked to modifiable risk factors – and thus could be preventable – according to a new study from American Cancer Society researchers. These figures, based on data from 2014, translate to:

• 659,640 cancer cases (out of 1,570,975), and
• 265,150 cancer deaths (out of 587,521). 

The researchers came up with the estimates by calculating how much certain lifestyle factors contributed to 26 different cancer types among adults ages 30 and older. These risk factors included:

• Cigarette smoking
• Secondhand smoke
• Excess body weight
• Drinking alcohol
• Eating red and processed meat
• Diet low in fruits and vegetables, dietary fiber, and dietary calcium
• Physical inactivity
• Ultraviolet (UV) radiation from the sun or indoor tanning
• 6 cancer-associated infections – Helicobacter pylori, hepatitis B virus (HBV), hepatitis C virus (HPC), human herpes virus type 8 (HHV8), human immunodeficiency virus (HIV), and human papillomavirus (HPV)

For the analysis, the researchers first looked at the prevalence of these known risk factors and their relative risk – that’s the extent to which the risk factors can increase cancer risk. They used that information to estimate the proportion of cancers associated with those risk factors. Then they applied those proportions to actual cancer diagnosis and death data to estimate the total numbers of associated cancer cases and deaths. The results were published Nov. 21 online in CA: A Cancer Journal for Clinicians.

The authors used data from the Centers for Disease Control and Prevention and the National Cancer Institute. The authors say their study improves upon past analyses because they included more risk factors and cancer types and they used nationally representative and up-to-date data.

The authors write that although the cancer mortality rate has declined by 25% since 1991, the overall cancer burden is still high. The American Cancer Society estimates that more than 1.6 million new cancer cases and 600,000 cancer deaths will occur in 2017. The researchers say their findings can help leaders set priorities for cancer prevention and control. 

Risk Factor Rankings

The authors analyzed each risk factor’s contribution to overall cancer cases and deaths in 2014. Cigarette smoking topped the list.   

1. Cigarette smoking accounted for 19% of all cancer cases and nearly 29% of cancer deaths
2. Excess body weight was responsible for 7.8% of cancer cases and 6.5% of deaths
3. Drinking alcohol was linked to 5.6% of cancer cases and 4% of deaths
4. UV radiation was attributable to almost 5% of cases, but a lower 1.5% of deaths
5. Physical inactivity played into 2.9% of cases and 2.2% of deaths

When the researchers grouped together the related issues of excess body weight, alcohol intake, poor diet, and physical inactivity, they found this set of risks was responsible for a total of about 18% of cancer cases and 16% of deaths. 

Cancer Type Comparisons

The researchers also looked at the 26 cancer types individually to find out which ones had the biggest links to the lifestyle risk factors. 

They found the proportion of cases linked to modifiable risk factors ranged from a high of 100% for cervical cancer and Kaposi sarcoma to a low of 4.3% for ovarian cancer. More than 75% of the melanoma, anal, lung, larynx, and oral cavity cancer cases and deaths could be attributed to modifiable risk facts. And the proportion of cancer cases connected to modifiable risk factors was greater than 50% for 15 of the 26 cancer types analyzed.

When looking at the total numbers of cancer deaths by type that were linked to modifiable risks:

• lung cancer was at the top for both men and women, with more than 132,960 deaths;
• colorectal cancer followed, again for both men and women, with 28,900 deaths;  
• liver cancer in men (9,860 deaths) and breast cancer in women (11,370 deaths) took the third spot.

Mapping Risks Factors to Cancer Types

The study detailed the extent to which each risk factor contributed to each cancer type.

Key Findings for Women and Men

The authors highlighted important differences by gender.

• The proportion of cancer cases and deaths linked to smoking, eating of red and processed meat, HCV infection, UV radiation, and HIV infection were higher in men than in women because historically these risk factors have been more prevalent among men.
• The proportion of cancer cases and deaths attributable to excess body weight, drinking alcohol, physical inactivity, and HPV infection were higher for women than men, which the authors say is “largely due to the high burden of breast, endometrial, and cervical cancers attributable to these risk factors.” 

Putting It All Together

The authors stated that doing more to increase the awareness and availability of prevention strategies that we already know work is vital to reducing the number of preventable cancers. They call out strategies such as taxing cigarettes to reduce smoking and increasing vaccination rates to protect against cancer-causing HPV infections.

Otis W. Brawley, MD, American Cancer Society chief medical officer and study co-author says this new study provides critical information that will help guide cancer and public health leaders in the years ahead.

Importantly, the researchers noted that modifiable risk factors might be responsible for even more cancer cases and deaths than they were able to estimate in their paper. The study's lead author, American Cancer Society researcher Farhad Islami, MD, PhD ,  explained: “We lacked nationally representative data for several other potentially modifiable risk factors...and, we did not consider many likely, but as-yet unestablished, associations between certain risk factors and other cancer types.”