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Risk for breast cancer from combination hormone therapy higher than previously thought
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The effect of combination menopausal hormone therapy on breast cancer risk may have been significantly underestimated, researchers from the United Kingdom reported.
Results of the Breast Cancer Now Generations Study, published in British Journal of Cancer, suggest that 775 of 39,000 women with a known age at menopause developed breast cancer by 6-year follow-up.
Women who reported taking combination hormone therapy (median duration, 5.4 years) were 2.7 times more likely to be diagnosed with breast cancer than those who reported never using hormone therapy.
“Our results show that risk of breast cancer increases with duration of use of combined menopausal hormone therapy up to 15 or more years,” Michael E. Jones, MD, PhD, staff scientist in the division of genetics and epidemiology at The Institute of Cancer Research in London, and colleagues wrote. “Relative risks in most of the published literature are likely to be substantially underestimated because of lack of updating therapy status through follow-up in cohort studies and inclusion of women with inferred menopausal age in cohort or case–control analyses. “These results provide further information to allow women to make informed decisions about the potential risks and benefits of menopausal hormone therapy use.”
HemOnc Today spoke with Jones about the results and their potential implications, given that most studies omit menopausal hormone therapy use after enrollment and many infer menopausal age.
Question: What prompted you and your c olleagues to conduct this study?
Answer: More than a decade ago, large studies like the Women’s Health Initiative and the Million Women Study helped to establish that combined estrogen plus progestogen menopausal hormone therapy increased the risk for breast cancer. However, menopausal hormone therapy continues to be used by many women, so accurate information is needed to balance risks and benefits. We knew that, in many previous cohort studies, risk for breast cancer in relation to combined menopausal hormone therapy was possibly underestimated because many studies did not take into account that women could stop use and their risk would drop back down to the level seen among nonusers. We had detailed information on menopausal hormone therapy use from women in the Breast Cancer Now Generations study, a large cohort study of more than 100,000 women in the United Kingdom that we intend to follow for decades to come. Using information from this cohort, we were able to estimate — more accurately, we believe — the risk for breast cancer in relation to menopausal hormone therapy use.
Q: What do the data suggest?
A: Women who used combined menopausal hormone therapy for a median duration of 5.4 years were 2.7 times more likely to develop breast cancer during the period of hormone therapy use than women who never used menopausal hormone therapy. This risk increased with duration of use, with women who had used combined therapy for more than 15 years being 3.3 times more likely to develop breast cancer than nonusers. The increased risk was found to return to about normal once hormone therapy use ended, confirming the findings of previous studies. Among women who used estrogen-only therapy, there were no overall increases in breast cancer risk compared with women who never used menopausal hormone therapy.
Q: What do you consider the take-home message ?
A: Combined menopausal hormone therapy increases the risk for breast cancer, and this risk increases with duration of use but reverts back to the level in nonusers a few years after cessation of use.
Q: Were you surprised by any of the findings?
A: We found that breast cancer risk was increased with other and unspecified types of menopausal hormone therapy, and because we did not see a trend with duration of use, we wonder if the raised risk is an intrinsic characteristic of the women being prescribed these types of menopausal hormone therapy rather than the type of menopausal hormone therapy itself — generally selective estrogen receptor modulators.
Q: What might future research entail?
A: Breast cancer risk may be different for serial vs. continuous combined menopausal hormone therapy, and this deserves further investigation. Risk in relation to selective estrogen receptor modulators also needs to be investigated.
Q : Is there anything else that you would like to mention ?
A: This piece of research is only one small part of the accumulating scientific literature on this topic. Clinical practice should be driven by recommendations from expert reviews and appraisals of the whole literature. – by Jennifer Southall
For more information:
Michael E. Jones, MD, PhD, can be reached at The Institute of Cancer Research, 123 Old Brompton Road, London SW7 3RP; email: michael.jones@icr.ac.uk.
Reference:
Jones ME, et al. Br J Cancer. 2016: doi:10.1038/bjc.2016.231.
Disclosure: Jones reports no relevant financial disclosures.