open access: Menopausal hormone therapy and breast cancer: what is the true size of the increased risk? (UK study)

British Journal of Cancer

  The BGS is a cohort study of 113 693 women from the United Kingdom, aged 16 years, from whom questionnaire information and informed consent was gained at recruitment during 2003–2015. The first follow-up questionnaire was completed at 2.5 years after recruitment, a second at ~6 years, and a third at 9.5 years. The study was approved by the South East Multi-Centre Research Ethics Committee.

Conclusions:

  Lack of updating MHT status through follow-up and inclusion of women with inferred menopausal age is likely to result in substantial underestimation of the excess relative risks for oestrogen plus progestogen MHT use in studies with long follow-up, limited updating of exposures, and changing or short durations of use.