Menopausal hormone therapy and breast cancer: what is the true size of the increased risk?

...Professor Baber (International Menopause Society President) concludes “This new observational study, with the best of intentions, remains an observational study with small numbers of breast cancer cases and dose not change our overall understanding of the relationship between MHT use and breast Cancer risk”....

For full comment see the Media article Menopausal hormone therapy and risk of breast cancer 

Abstract

Background:
Menopausal hormone therapy (MHT) increases breast cancer risk; however, most cohort studies omit MHT use after enrolment and many infer menopausal age.

Methods:
We used information from serial questionnaires from the UK Generations Study cohort to estimate hazard ratios (HRs) for breast cancer among post-menopausal women with known menopausal age, and examined biases induced when not updating data on MHT use and including women with inferred menopausal age.

Results:
Among women recruited in 2003-2009, at 6 years of follow-up, 58 148 had reached menopause and 96% had completed a follow-up questionnaire. Among 39 183 women with known menopausal age, 775 developed breast cancer, and the HR in relation to current oestrogen plus progestogen MHT use (based on 52 current oestrogen plus progestogen MHT users in breast cancer cases) relative to those with no previous MHT use was 2.74 (95% confidence interval (CI): 2.05-3.65) for a median duration of 5.4 years of current use, reaching 3.27 (95% CI: 1.53-6.99) at 15+ years of use. The excess HR was underestimated by 53% if oestrogen plus progestogen MHT use was not updated after recruitment, 13% if women with uncertain menopausal age were included, and 59% if both applied. The HR for oestrogen-only MHT was not increased (HR=1.00; 95% CI: 0.66-1.54).

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.

Reference

Jones ME, Schoemaker MJ, Wright L, McFadden E, Griffin J, Thomas D, Hemming J, Wright K, Ashworth A, Swerdlow AJ. Menopausal hormone therapy and breast cancer: what is the true size of the increased risk? Br J Cancer. 2016 Aug 23;115(5):607-15. doi: 10.1038/bjc.2016.231. Epub 2016 Jul 28.

Content updated 25 August 2016