In a recent study published in CA: A Cancer Journal for Clinicians, a team of researchers analyzed nationally representative cancer incidence, risk factor prevalence, and mortality data to determine the number and proportion of various types of cancer cases and cancer-related mortality that could be attributed to modifiable risk factors.

Study: Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States, 2019. Image Credit: africa_pink / Shutterstock

Background

Despite substantial resources and efforts being invested in cancer research and an improved understanding of the mechanisms and pathology of cancer, the economic and health burden of cancer remains significant. A 2018 study by the same team of researchers examined the proportion of cancer cases and mortality that were attributable to modifiable risk factors, intending to improve cancer awareness and advocate for changes to control or prevent various types of cancer.

These modifiable risk factors include dietary and exercise-related factors, smoking behavior, alcohol consumption, exposure to ultraviolet (UV) radiation, as well as infections with various pathogens such as human papillomavirus (HPV), hepatitis B and C viruses, Epstein–Barr virus (EBV), Helicobacter pylori, and human immunodeficiency virus (HIV). However, new data has emerged since 2018 on the magnitude and nature of the associations between many of these modifiable risk factors and the risk of cancer, warranting a re-examination.

About the study

The present study analyzed cancer occurrence data from 2019 to evaluate the number and proportion of cases and deaths for 30 types of cancers (except for excluding non-melanoma skin cancers) and their association with a wide range of modifiable risk factors.

Despite the availability of data from 2020, the researchers used 2019 data to circumvent the low cancer diagnosis rates after cancer screening programs and diagnostic facilities were suspended or reduced due to the coronavirus disease 2019 (COVID-19) pandemic.

Data on new cases of invasive cancer from 2019 were obtained from cancer registries and surveillance programs run by the United States (U.S.) Centers for Disease Control and Prevention (CDC) and the National Cancer Institute. Data obtained from National Health and Nutrition Examination surveys from 2007 to 2016 were used to determine various modifiable risk factors.

A comprehensive list of modifiable risk factors was examined, including former and current smoking, body weight, low physical activity levels, exposure to second-hand smoke, increased consumption of processed and red meats, alcohol intake levels, and low intake of dietary fibers, dietary calcium, vegetables, and fruits.

While smoking is linked to numerous types of cancer, exposure to second-hand smoke increases the risk of bronchus and lung cancers. Dietary factors are predominantly associated with increased risk of colorectal cancer. Furthermore, UV radiation is a known risk factor for melanomas, and excess body weight, alcohol consumption, physical inactivity, and cigarette smoking are risk factors for multiple types of cancers.

Infections with H. pylori and viruses such as hepatitis B and C viruses, HPV, HIV, EBV, and Kaposi sarcoma herpesvirus were also included in the list of modifiable risk factors. Hepatitis B and C viruses are known risk factors for hepatic cancers, while EBV is linked to Hodgkin lymphoma and nasopharynx cancer. Helicobacter pylori infections are known to increase the risk of stomach cancer, and HPV infections are associated with various types of cancers, including cervical cancer.

Results

The study found that 40% of all cancer cases in 2019, not including the non-melanoma forms of skin cancer, in adults above 30 years of age in the U.S. were due to modifiable risk factors. Furthermore, modifiable risk factors were also responsible for 44% of all cancer-related mortality in adults older than 30 years.

Cigarette smoking was linked to the greatest number of cancer cases (19.3%) and mortality (28.5%), with excess body weight and alcohol consumption being the next two predominant causes of cancer and cancer-related deaths.

Of the 30 types of cancers evaluated in the study, 19 forms of cancer had over half the cases and deaths associated with modifiable risk factors. The majority of cancer cases and deaths due to modifiable risk factors were lung cancer.

Breast cancer in women, melanomas, and colorectal cancer were responsible for the next three highest number of cancer cases attributed to modifiable risk factors. Apart from lung cancer, the highest number of cancer-related deaths attributed to modifiable risk factors were colorectal, liver, and esophageal cancer, in that order. The researchers noted that in comparison to the results from the previous study, there was an increase in the types of cancers associated with excess body weight.

Conclusions

Overall, the study found that almost 40% of all cancer cases in the U.S. in 2019 and close to 44% of cancer-related deaths could be attributed to modifiable risk factors, with cigarette smoking being the significant risk factor. Lung cancer was the predominant form of cancer attributed to modifiable risk factors.

The results emphasized that a growing number of cancer cases and mortality are linked to modifiable risk factors, and implementing lifestyle changes such as avoiding smoking, reducing alcohol and red and processed meat consumption, achieving adequate physical activity levels, and eating a healthy diet can substantially lower the overall cancer burden.