Reproductive factors in relation to incidence of lung and colorectal cancers in a Norwegian women cohort: the HUNT Study

Abstract

Abstract Background The roles of reproductive factors in the aetiology of lung and colorectal cancers, among the most common cancers in women, are unclear. Methods We followed up 33,314 cancer-free women who participated in the HUNT Study in Norway from 1995-1997 to 2018. A large panel of reproductive factors were self-reported at baseline. Incident lung and colorectal cancer cases were ascertained from the Cancer Registry of Norway. Cox regression models were used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs) after adjustment for important confounders. Results During a median follow-up of 22.2 years, 467 women developed lung cancer including 169 lung adenocarcinoma, 660 developed colon cancer and 211 had rectal cancer. Early menarche (≤12 years) was associated with an increased incidence of lung adenocarcinoma (HR 1.43, 95% CI 1.02–2.03). Women with one or no child had an increased colon cancer incidence (HR 1.26, 95% CI 1.03–1.54). Hormone therapy appeared to be associated with a decreased incidence of rectal cancer (HR 0.68, 95% CI 0.44–1.04). Results in the subgroup of post-menopausal women were similar or strengthened. Other reproductive factors were not related to the risk of lung, colon, and rectal cancers. Conclusions Certain reproductive factors might play a role in the aetiology of lung and colorectal cancers. Further investigations are warranted to study if they are causal associations.