In a reversal of historic trends, researchers at the American Cancer Society (ACS) have found higher lung cancer incidence in women than in men between the ages of 35 and 54.
Mark Dylewski, M.D., chief of general thoracic surgery at Baptist Health Miami Cancer Institute.
The findings, published by the American Cancer Society in JAMA Network, also contradict a common perception that lung cancer occurs mostly in middle-aged or older men who have smoked for many years. Overall, the rates of lung cancer have been falling in the U.S. There were about 65 new cases of lung cancer for every 100,000 people in 1992. By 2019, that figure had dropped to about 42.
The cited disparity in the new study is not large — about one or two more cases among every 100,000 women in that age range compared to men. But researchers emphasize that more studies are needed. Overall, lung cancer remains the leading cause of cancer death nationwide. The U.S. Centers for Disease Control and Prevention (CDC) states that about 197,000 people are diagnosed with lung cancer every year.
In a separate report released this month, the American Lung Association put out its 2023 “State of Lung Cancer” update, finding that the rate of lung cancer screening in Florida “is far too low at 2.4 percent, compared to the national average of 4.5 percent.” Overall, lung cancer survival rates have increased over the past five years, but serious disparities remain among Black and Hispanic/Latino communities in Florida and across the nation, the report finds. Nationally, the report found that only 4 percent of women considered high risk for lung cancer were screened.
The new study by the American Cancer Society found that cigarette smoking did not necessarily affect women more than men. However, smoking is, by far, the leading cause of lung cancer. The survival rate for lung cancer that has not spread is now more than 50 percent in the U.S, but lung cancer is often diagnosed in later stages after it has spread.
“This is an epidemiology study looking at the incidence of lung cancer in men and women in the various age groups,” explains Mark Dylewski, M.D., chief of general thoracic surgery at Baptist Health Miami Cancer Institute. “And what the study found is that we are seeing a decrease in lung cancer patients for various reasons overall across the United States. We're smoking less frequently and less patients are adopting combustible tobacco at earlier ages. So, we’re going to ultimately see a trend in the downward incidence of lung cancer. However, what was shown in this particular study is that women in particular are seeing less of a reduction in the incidence of lung cancer.”
Manmeet Ahluwalia, M.D., chief of medical oncology, chief scientific officer, and deputy director of research at Baptist Health Miami Cancer Institute.
Researchers analyzed population-based incidence data on lung and bronchus cancers diagnosed from 2000 to 2019 from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program. The data covered nearly 50 percent of the U.S. population. The results showed the declines in lung cancer incidence rates between 2000-2004 and 2015-2019 were greater in men than women, leading to higher incidence in women aged 35-54 years.
Among individuals aged 50-54 years, for example, the rate per 100,000 person-years decreased by 44 percent in men, compared to 20 percent in women, the study found.
“So, men had a hundred percent decrease in instance of lung cancer in that age group compared to females, which is very disturbing, for one,” said Dr. Dylewski. “And it's hard to understand the details of what led to that significant reduction in the incidence of lung cancer in men compared to women.”
What precisely is causing the disparity in lung cancer incidence between men and women in this age range is not known at this time. Other recent research data indicates that non-smoking related risk factors for lung cancer are fueling cases among younger adults, explains Manmeet S. Ahluwalia, M.D., M.B.A, FASCO, chief of medical oncology, chief scientific officer, and deputy director of research at Miami Cancer Institute and Baptist Health Cancer Care, and Fernandez Family Foundation Endowed Chair in Cancer Research.
“There is a greater incidence of women being diagnosed at an early stage of lung cancer not related to smoking, and most of them are oncogenic driven (via genetic mutation such as EGFR (epidermal growth factor receptor) tumors,” said Dr. Ahluwalia.
EGFR-positive lung cancer represents about 10-15 percent of lung cancer cases in the U.S., and generally appears in adenocarcinoma subtype of non-small cell lung cancer, according to the American Lung Association. Patients with lung cancers with EGFR mutations tend to have minimal to no smoking history.
New research even points to air pollution particles as a potential cause of EGFR mutant lung cancer. “Increasing exposure to 2.5 µm particulate matter (PM2.5) increases the risk of non-small cell lung cancer in non-smoking individuals with EGFR mutations,” explains Dr. Ahluwalia.
Nonetheless, the precise cause of young women outpacing young men in lung cancer rates remains somewhat of a mystery while the topic fuels ongoing research.
“The cause may be multifactorial,” adds Dr. Dylewski. “I doubt very much that women are starting to smoke more frequently than men, but it also may be hormonal, or it may be environmental. We know that there's an increased instance of adenocarcinoma in women between the ages of 50 and 74 that are completely unrelated to smoking and are found in non-smokers. And that may have some influence. But we don't quite understand why we're seeing an increase in incidence in non-smoking women in that age group.”