BMJ Open;Volume 7, Issue 11
BMJ Publishing Group
Objectives: With the present study, we aimed to investigate the association between menopausal hormone therapy (HT) and risk of colorectal cancer (CRC). Setting: Cohort study based on the linkage of Norwegian population-based registries. Participants: We selected 466822 Norwegian women, aged 55–79, alive and residing in Norway as of 1 January 2004, and we followed them from 2004 to 2008. Each woman contributed person-years at risk as non-user, current user and/or past HT user. Outcome measures: The outcome of interest was adenocarcinoma of the colorectal tract, overall, by anatomic site and stage at diagnosis. Incidence rate ratios (RRs) with 95% CIs were estimated by Poisson regression and were used to evaluate the association between HT and CRC incidence. Results: During the median follow-up of 4.8 years, 138 655 (30%) women received HT and 3799 (0.8%) incident CRCs occurred. Current, but not past, use of HT was associated with a lower risk of CRC (RR 0.88; 95% CI 0.80 to 0.98). RRs for localised, regionally advanced and metastatic CRC were 1.13 (95% CI 0.91 to 1.41), 0.81 (95% CI 0.70 to 0.94) and 0.79 (95% CI 0.62 to 1.00), respectively. RRs for current use of oestrogen therapy (ET) were 0.91 (95% CI 0.80 to 1.04) while RR for current use of combined oestrogen–progestin therapy (EPT) was 0.85 (95% CI 0.70 to 1.03), as compared with no use of HT. The same figures for ET and EPT in oral formulations were 0.83 (95% CI 0.68 to 1.03) and 0.86 (95% CI 0.71 to 1.05), respectively. Conclusions: In our nationwide cohort study, HT use lowered the risk of CRC, specifically the most advanced CRC.
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