Parity and risk of lung cancer in women.

B210

Background: Epidemiologic patterns of lung cancer incidence suggest that women may be at increased risk for lung cancer as compared to men after controlling for smoking and other factors. Reproductive lifestyle factors could in part explain the apparent increased susceptibility of lung cancer among females. Given the role of estrogen in the etiology of other cancers, and the relationship between number of births and endogenous estrogen levels, we hypothesized that parity may be associated with lung cancer risk in women. Methods: Data from 1075 female cases and 867 female controls enrolled in the Lung Cancer Susceptibility Study at the Massachusetts General Hospital from 1992 through 2004 were available for the main analysis of the association between parity (parous vs. nulliparous) and lung cancer risk. Information on number of children was available for the subset of this population recruited for the study between 1992 and 2002, comprising 689 cases and 788 controls. Multivariate logistic regression was used to estimate adjusted odds ratios (OR) and their 95% confidence intervals (95% CI). Results: Nulliparity was more prevalent among cases as compared to controls, corresponding to a statistically significant crude odds ratio of 0.63 (p <0.001, 95% CI: 0.51, 0.79) for prior childbearing. After controlling for age, smoking status, pack-years, and years since smoking cessation, the adjusted OR was 0.54 (95% CI 0.41, 0.70). A significant linear trend was found for decreasing risk of lung cancer associated with increasing numbers of children (p<0.001). While the risk associated with having one child was similar to the risk for nulliparous women (OR=1.04, 95% CI 0.63, 1.73), an increasingly protective effect was observed among women with 2 (OR=0.81, 95% CI 0.54, 1.21) and 3+ children (OR=0.59, 95% CI 0.40, 0.85). An analysis of the interaction between smoking status (ever-smokers vs. never-smokers) and parity with lung cancer risk suggested that the protective effect of prior childbearing was stronger in those women without a history of active smoking, although this finding was not statistically significant (p=0.074). The inverse association between parity and lung cancer risk was not observed in early onset cases (age <55 years at diagnosis), and was limited to cases of average age of onset (p=0.0013). Conclusions: Our data offer support for an inverse association between having children and risk of lung cancer among women, and a trend of increasing protection with greater numbers of births. This work was supported by NIH Grants R01CA74386 and T32ES07069.