MORE LUNG CANCER IN YOUNG WOMEN THAN MEN

It's official: In the United States, the incidence of lung cancer in young women has now surpassed that of their male counterparts, a collaborative study between the American Cancer Society (ACS) and the National Cancer Institute (NCI) shows.

A report of the study was published online May 22 in the New England Journal of Medicine.

This study "confirms that some of the trends we have been seeing in the oncology clinic over the last few years are true. The research shows that yes, lung cancer is affecting more and more women of younger and younger ages," said Lecia V. Sequist, MD, MPH, associate professor of medicine at Harvard Medical School and attending physician at Massachusetts General Hospital in Boston. She was not involved in the study and was approached for comment. 

The study analyzed data from the North American Association of Central Cancer Registries, which covers 96% of the US population. The analysis showed that in the 20-year period between 1995 and 2014, the overall incidence of lung cancer decreased in both men and women. However, in women of white and Hispanic origin who were born in 1965 or later, the analysis shows that the female-to-male incidence rate ratios exceeded 1.0 for the first time.

Lung cancer mortality rates in young white and Hispanic women approached or equaled those of men but didn't cross over, say Ahmedin Jemal, PhD, from the American Cancer Society, Atlanta, Georgia, and colleagues.

In white women 40 to 44 years of age, the incidence rate ratio increased from 0.88 between 1995 and 1999 to 1.17 between 2010 and 2014. During the same time periods, the female-to-male incidence rate ratio in Hispanic women jumped from 0.79 to 1.22.

Similarly, in white adults age 45 to 49 years, the female-to-male incidence rate ratio increased from 0.81 to 0.83 in the cohort born around 1950, and to 1.13 in the cohort born around 1965. In Hispanic adults, this ratio increased from 0.64 to 0.72 in those born around 1950 to 1.12 in those born in the mid-1960s.

The sex-based crossover in female-to-male incidence ratios is "especially remarkable" in the Hispanic population because "smoking prevalence among its young adults is substantially lower among women than men," the researchers say.

They point out that the overall number of women who smoke has not exceeded the number of male smokers, and that on average, women smoke fewer cigarettes per day than men. Women are also less likely than men to use tobacco products such as cigars and chewing tobacco, they add.

These sex differences in smoking behaviors do not fully account for the historic reversal in female-to-male incidence rate ratios, Jemal and colleagues say. Nevertheless, this finding has important implications for public health, they add.

"It may foreshadow a higher future burden of overall lung cancer among women than among men as younger cohorts age, which further underscores the need to intensify antitobacco measures to decrease smoking among young women," the authors write. "Our finding also calls for continued monitoring of sex-specific risks of lung cancer and for etiologic studies, including studies of sex differences in smoking-related susceptibility to lung cancer, to identify reasons for the higher rates of lung cancer among young women."

Although the age-specific incidence of lung cancer has been declining for the past two decades in both men and women 30 to 54 years of age across all races and ethnic groups, these declines have been steeper in men, the investigators note. Cigarette smoking contributes to about 80% of the 154,000 lung cancer deaths that occur in the United States each year, and cancers of the lung and bronchus remain the country's top causes of preventable cancer death, they point out.

Commenting on the findings, Sequist agreed that more research is needed to understand the reasons behind the trends that were revealed by the new study.

"More than ever we need better early detection methods that can reach broader populations," she told Medscape Medical News. "Smoking cessation is not the only tool to prevent lung cancer, since an increasing number of cases are being diagnosed in never-smokers."

For the study, Jemal and colleagues examined the nationwide population-based incidence of lung cancer and calculated the age-specific incidence of lung cancer per 100,000 person-years, as well as female-to-male incidence rate ratios according to sex, race or ethnic group, and histologic type. They also looked at age group from 30 to 54 years, birth years from 1945 to 1980, and calendar period of diagnosis from 1995 to 2014. Data from the National Health Interview Survey from 1970 to 2016 were used to determine the prevalence of cigarette smoking.

The fact that women have been slower than men to quit smoking may be contributing to the increasing female lung cancer incidence rates, they suggest. More frequent detection of indolent lung tumors in women than in men through screening or diagnostic imaging could also explain the higher rates of lung cancer among women.

Lung cancer may also progress more slowly in women than in men, Jemal and colleagues point out. A recent study of baseline CT screening for lung cancer in North America showed that the prevalence of lung cancer among women was nearly twice as high as that among men of similar age and with similar smoking history, they note.

This study was funded by the American Cancer Society. The authors have disclosed no relevant financial relationships.