Eighteen studies were included in the review: three RCTs, six cohort studies, one nested case-control study and eight case-control studies.
Ever use of hormone therapy (17 studies):
Ever use of hormone therapy (any type) was associated with a significant decrease in the risk of all subtypes of lung cancer (RR 0.80, 95% CI 0.72 to 0.89; eight studies). When analysis was stratified according to type of cancer there was no association between hormone therapy and adenocarcinoma (four studies), small cell carcinoma (three studies) and squamous carcinoma (two studies). There was an increased risk of non-small cell carcinoma (RR 0.71, 95% CI 0.61 to 0.82; four studies). There was no evidence of heterogeneity (I2=0%) for any of these analyses.
When the analysis was restricted to non-smokers (seven studies) or to smokers (six studies) there was no association between hormone therapy and all subtypes of lung cancer. However, there was an increased risk of adenocarcinoma in non-smoking women (RR 1.76, 95% CI 1.07 to 2.90; two studies). Use of oestrogen therapy and all subtypes of lung cancer was associated with a decreased risk of lung cancer (RR 0.73, 95% CI 0.61 to 0.87; three studies). Use of oestrogen/progestin therapy was not associated with lung cancer risk for all studies combined (five studies), but was associated with an increased risk when the analysis was restricted to the two RCTs (RR 1.36, 95% CI 1.03 to 1.79).
Duration of use of hormone therapy (four studies):
Two studies that reported data for all subtypes of lung cancer combined reported a small but significant decrease of risk (4.7% per year of hormone therapy use). There was no significant difference in risk for three studies that assessed adenocarcinoma. Stratification based on smoking status did not provide significant findings.