Use of exogenous hormones by women and lung cancer: evidence from the Royal College of General Practitioners' Oral Contraception Study.

OBJECTIVE

The objective of this study was to assess the risk of lung cancer among women who have used oral contraception or hormone replacement therapy (HRT), especially those exposed to both classes of exogenous hormones.

DESIGN

This study is a nested case-control one using prospectively collected data from the Royal College of General Practitioners' Oral Contraception Study (OCS). The 162 case patients were women with a diagnosis of lung cancer recorded on the OCS database by August 2004. Each case patient was matched with 3 control subjects who were free of the disease at the time of the case patient's diagnosis, of similar age and with similar length of follow-up in the OCS.

RESULTS

Compared with never use, current use of oral contraception was associated with a statistically nonsignificant reduced risk of lung cancer, with an adjusted odds ratio (OR) of 0.47 and a 95% confidence interval (CI) of 0.08-2.95 (OR=0.86 and 95% CI=0.50-1.48 for former use; OR=0.84 and 95% CI=0.49-1.43 for ever use). Similar comparisons for HRT were current use (OR=1.21, 95% CI=0.23-6.37), former use (OR=0.62, 95% CI=0.23-1.68) and ever use (OR=0.71, 95% CI=0.28-1.78). The OR among women who had used both classes of hormones was 0.53 (95% CI=0.16-1.72), as compared with those who had used neither.

CONCLUSIONS

Our results are compatible with findings from other studies that suggest that oral contraceptives may reduce the risk of lung cancer. Evidence for a beneficial effect of HRT is less convincing. Further study is needed to determine how long any benefit lasts and whether it is stronger in women exposed to both classes of exogenous hormones. The small number of events occurring in this very large cohort, however, shows that any public health benefit is likely to be marginal.