Why are healthy young non-smokers developing lung cancer?

But new research from the USC Norris Comprehensive Cancer Center, part of Keck Medicine of USC, suggests an unexpected possibility. Findings presented at the annual meeting of the American Association for Cancer Research indicate that younger Americans under age 50 who have never smoked and consume more of these healthy foods than average may face a higher risk of developing lung cancer.

"Our research shows that younger non-smokers who eat a higher quantity of healthy foods than the general population are more likely to develop lung cancer," said Jorge Nieva, MD, a medical oncologist and lung cancer specialist with USC Norris and lead investigator of the study. "These counter-intuitive findings raise important questions about an unknown environmental risk factor for lung cancer related to otherwise beneficial food that needs to be addressed."

Researchers Suspect Pesticide Exposure May Play a Role

The researchers emphasize that the foods themselves are not believed to be the problem. Instead, they suspect pesticide exposure could help explain the surprising pattern.

According to Nieva, commercially grown (non-organic) fruits, vegetables, and whole grains generally contain higher levels of pesticide residues than dairy products, meat, and many processed foods. He also pointed to previous research showing that agricultural workers with long term pesticide exposure experience higher rates of lung cancer, adding support to the hypothesis.

The study also found that women under 50 who have never smoked develop lung cancer more often than men in the same age group. Women in the study also tended to eat more fruits, vegetables, and whole grains than their male counterparts.

Rising Lung Cancer Cases in Young Non-Smokers

Lung cancer has traditionally been associated with older adults, smokers, and men. The average age at diagnosis is 71.

Although smoking rates have steadily declined since the mid 1980s, helping reduce lung cancer cases overall in the United States, one group has not followed that trend. Lung cancer has become more common among non-smokers age 50 and younger, particularly women, who are now more likely than men in the same age group to develop the disease.

To better understand why, researchers launched the Epidemiology of Young Lung Cancer Project. The study included 187 people who had been diagnosed with lung cancer by age 50. Participants provided information about their diet, smoking history, demographics, and cancer diagnosis.

Most had never smoked and were diagnosed with a form of lung cancer that differs biologically from the type typically caused by tobacco use. A 2021 study from the Epidemiology of Young Lung Cancer Project, the Genomics of Young Lung Cancer Project, also found that lung cancers diagnosed in people younger than 40 represent distinct subtypes compared with those seen in older adults.

Healthier Diets Were Common Among Patients

Researchers compared participants' diets with those of the general U.S. population using the Healthy Eating Index (HEI), a measure of overall diet quality scored from 1 to 100.

The young non-smoking lung cancer patients had an average HEI score of 65, compared with the national average of 57. Women in the study generally scored higher than men.

Participants also reported eating more fruits, vegetables, and whole grains than the average American. On average, they consumed 4.3 daily servings of dark green vegetables and legumes and 3.9 servings of whole grains. By comparison, the typical U.S. adult consumes 3.6 servings of dark green vegetables and legumes and 2.6 servings of whole grains each day.

More Studies Are Needed

Nieva stressed that the proposed connection between pesticide exposure and lung cancer remains unproven and requires additional investigation, especially among younger adults and women.

The researchers did not directly measure pesticide levels in individual foods eaten by participants. Instead, they estimated exposure using previously published data on average pesticide residues found in food categories such as fruits, vegetables, and grains.

The next phase of the research will involve measuring pesticide levels directly in patients' blood or urine samples. That work could help determine whether certain pesticides are more strongly associated with lung cancer risk than others.

"This work represents a critical step toward identifying modifiable environmental factors that may contribute to lung cancer in young adults," said Nieva. "Our hope is that these insights can guide both public health recommendations and future investigation into lung cancer prevention."

The research was supported by the Addario Lung Cancer Medical Institute, a nonprofit organization dedicated to advancing lung cancer research and care, along with AstraZeneca, the Beth Longwell Foundation, Genentech, GO2 for Lung Cancer, and Upstage Lung Cancer.

Additional funding came from the National Institutes of Health through grant number R25CA225513 and the National Cancer Institute through grant number P30CA014089.