Researchers from Wayne State University concluded that there is a weak association between lung cancer risk and reproductive history or hormone use. The study entitled  “Hormone Use, Reproductive History and Risk of Lung Cancer: The Women’s Health Initiative Studies” was published on April 3, 2015 in the Journal of Thoracic Oncology, the official journal of the International Association for the Study of Lung Cancer.

Statistics show that of the total number of lung cancer deaths in the United States, 40% are women. Among the total lung cancer deaths in America, 90% of men who died from the disease developed lung cancer by smoking. However, for women who died from lung cancer, only 75-80% of them had smoked. Other gender differences include the higher risk of lung cancer in never-smoker women compared to never-smoker men, histological differences in lung cancer between the two genders and better prognosis in female compared to male (5-year survival rate of 20% compared to 15.4% for men).

A previous study from Women’s Health Initiative (WHI) and clinical trials (CT) showed no association between lung cancer and hormone therapy in postmenopausal women. Now, researchers studied the association between lung cancer risk and estrogen-related factors such as reproductive history, oral contraceptive use, and hormone therapy replacement. The study enrolled a geographically and ethnically diverse cohort of 161,808 postmenopausal women (50-79 years) between 1993 and 1998 across the United States and followed them for 14 years. Incident lung cancer was observed in 2,467 of them. Women who used estrogen plus progestin for less than 5 years had a slight decrease in lung cancer risk. There was also a trend towards decreased risk of lung cancer with increasing age at menopause, and with age 20-29 at first live birth. By contrast, there was a slight increased risk with increasing number of live births. The estimated risk varied with smoking history, years of hormone therapy and removal surgery of both ovaries.

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The authors concluded that “our study does not support the idea that reproductive history independently contributes to lung cancer risk, and recapitulates the inconsistent findings within epidemiological literature on lung cancer risk and reproductive history measures. Likewise, the epidemiologic literature is also inconsistent with regard to the role of hormone use in lung cancer risk and the overall results presented by our study suggest that oral contraceptives and hormone therapy use are not associated with risk of lung cancer,” said the lead author Ann G. Schwartz. “Questions remain about estrogen and lung cancer risk that will not easily be answered by studies focusing on hormone use and emphasizes that the interplay between cigarette smoking, estrogen, genetic susceptibility and lung cancer is complex and continued study is necessary to tease apart these relationships,” she added.