Breast cancer risk associated with HRT increases with longer use, finds studyBMJ 2019; 366 doi: https://doi.org/10.1136/bmj.l5332 (Published 30 August 2019) Cite this as: BMJ 2019;366:l5332
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Interestingly, although not mentioned in the main body of the article, the Lancet meta-analysis found that the relative risk for <5 years use of oestrogen + micronized (natural) progesterone was 0.91, i.e. 9% lower than for never-users of MHT (1) , which suggests that that this combination is safe at least for short duration of use, and should therefore be the preferred MHT preparation prescribed for relief of menopausal symptoms.
1. Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence. Lancet. 2019. www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)31709-X (appendix Figure S15, p. 45)
Competing interests: No competing interests
The HRT - breast cancer data from The Collaborative Group on Hormonal Factors in Breast Cancer reported in The Lancet this week is not surprising.1 What it suggests is that the cumulative exposure to HRT is the predominant risk for increased breast cancer risk. This is at a population level and not taking into account oestrogen receptor sensitivity and family history which increases the risk in individuals with these risks.
What the study or meta-analysis does not consider is the cumulative lifetime exposure to extraneous female hormones. There is great variation in women at 50 years of age from the point of view of hormone exposure to date. Many have taken the contraceptive pill or hormonal contraception for years and others not. In this meta-analysis they all start from baseline at age 50 or thereabouts and their hormone exposure to date is not considered as a confounding factor as regards subsequent cancer risk. Some if not the majority, would have heightened risk to start with from years of hormonal contraception. As the HRT study shows, the risk continues for years after stopping HRT and there is no reason to think that contraceptive hormonal exposure behaves any differently. Thus, those who took hormonal contraception for years are at more risk when they add to the hormonal load by taking HRT later in life. What is required is a comprehensive cumulative index of lifetime hormonal exposure or hormonal load from teens to 60s or 70s to correlate genuine cancer risk versus hormonal cumulative load. This is not even taking into account the behaviour of hormones in young women as compared to older post-menopausal women. Hormones may confer greater risk in reproductive age women for example the vast numbers of young women with invasive breast cancer cannot be understood except by attributing the enormous risk to hormone exposure from contraceptive sources.2 The sooner the real risks associated with hormone use is clarified the better for women of all ages.
1. Collaborative Group on Hormonal factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence. Lancet: https://doi.org/10.1016/S0140-6736(19)31709-X
2. Breen EG. The Screech Owls of Breast Cancer. Authorhouse 2013.
Competing interests: I wrote a book about hormones and breast cancer "The Screech Owls of Breast Cancer".Authorhouse 2013.