As women have become more like men in their smoking habits and a greater proportion of men abandon the habit, lung cancer has become the leading cause of cancer deaths among women in the U.S., resulting in more deaths annually than breast, uterine, and ovarian cancer combined.
While the rise in female lung cancer has been attributed to the increase in smoking among women, 20 percent of women who develop the diseases in the U.S. have never smoked. Fifteen to 20 percent of lung cancers occur in individuals who have never smoked, but 70 percent to 80 percent of people who “never smoked” are women.
According to the NCI, combined trends in lung cancer incidence and mortality rates have closely mirrored historical patterns of smoking prevalence, after accounting for an appropriate latency period. Because of historical differences in smoking prevalence between men and women, lung cancer rates in men have been consistently declining since 1990. The incidence rate in men declined from a high of 102.1 cases per 100,000 men in 1984 to 82.7 cases per 100,000 men in 2009, but consistent declines in women have not yet been observed.
In 2013, the National Cancer Institute estimates that 72,220 deaths will occur among U.S. women due to lung cancer, compared with 39,620 deaths due to breast cancer alone.
As the NCI notes, the reason for the increase in deaths among women can’t be attributed solely to increased smoking among women. Patricia Thistlethwaite, M.D., Ph.D., a cardiothoracic surgeon at the University of California at San Diego explained women are younger at the time of diagnosis of lung cancer than men, the proportion of adenocarcinoma and bronchoalveolar carcinoma is higher in women than in men, and women are less likely to have a smoking history. The cause for the “huge increase” in these two types of cancers among women is not known and is under investigation.
And scientists are looking for molecular differences characterizing lung cancers that may be responsible for increased susceptibility in women. Women exhibit decreased DNA repair capability and increased mutations in specific cancer genes such as p53, epidermal growth factor receptor (EGFR), and K-ras. Mutations in these genes are found at a much higher frequency in adenocarcinomas, particularly in women.