Hormone replacement therapy and lung cancer risk: a case-control analysis.

PURPOSE To date, there are few published data regarding the use of hormone replacement therapy (HRT) and lung cancer risk. Therefore, we analyzed data regarding HRT use from a large case-control study designed to study genetic susceptibility to lung cancer to determine whether HRT affected risk of lung cancer. EXPERIMENTAL DESIGN In a secondary analysis, we compared self-reported HRT use among 499 women with lung cancer and 519 healthy age-matched controls. RESULTS HRT use was associated with an overall reduced risk of 34% [odds ratio (OR), 0.66; 95% confidence interval (CI), 0.51-0.89] of lung cancer, after adjusting for age, ethnicity, smoking status, education, body mass index, and menopausal status. The use of estrogen replacement therapy alone was associated with a 35% reduction in lung cancer risk (OR, 0.65; 95% CI, 0.47-0.89) and the use of combination therapy (estrogen and progestin) was associated with a 39% reduction in lung cancer risk (OR, 0.61; 95% CI, 0.40-0.92). HRT use was also associated with a statistically significantly reduced risk of lung cancer in current smokers (OR, 0.59; 95% CI, 0.38-0.92), but the risk estimates were not statistically significant in never (OR, 0.72; 95% CI, 0.37-1.40) or former smokers (OR, 0.73; 95% CI, 0.46-1.15). In addition, as the cigarette pack-years increased among ever smokers, the protective effect diminished, so that light smokers appeared to benefit the most from HRT use. Decreased lung cancer risks were also evident when the data were stratified by age, ethnicity, and body mass index. The joint effects of HRT use and mutagen sensitivity suggest that HRT use modifies lung cancer risk for genetically susceptible women. HRT use was also associated with a lower risk of death and improved survival compared with the women not taking HRT. To provide a possible biological mechanism to explain our findings, we compared plasma levels of insulin-like growth factor I in users and nonusers, and demonstrated that HRT use was associated with statistically significantly lower insulin-like growth factor I levels for both cases and controls compared with non-HRT users. CONCLUSIONS These data suggest an association of HRT use with a decrease in lung cancer risk. However, there are several limitations to this secondary analysis, requiring that the data be viewed with caution, and confirmation is required in well-designed hypothesis driven studies. The biological role of HRT in lung cancer remains understudied, and only extensive research can yield new insights into the mechanisms underlying a protective effect of HRT for lung cancer.