The British Medical Journal recent published a paper on the findings of a study to assess the risks of breast cancer associated with different types and durations of hormone replacement therapy (HRT).

The study, the largest of its kind, involved 98,611 women aged 50-79 with a primary diagnosis of breast cancer between 1998 and 2018. Information was obtained from two large databases in UK primary care.

Dr Yana Vinogradova, a Senior Research Fellow in the School of Medicine at the University of Nottingham was the lead investigator on the study. She said: “Our purpose was to conduct the largest observational study ever undertaken, and to include all available information on HRT use and other risk factors. Our aim was to provide comprehensive, detailed and accurate estimates of the risks for different HRT treatment formulations.”

  • The study confirmed increased risks of breast cancer associated with long term use of oestrogen only therapy and combined oestrogen and progestogen therapy.
  • As shown by other studies, the risk was greater with combined HRT than with estrogen only, and the combined treatment associated with the lowest risk increase was estradiol-dydrogesterone.
  • The findings suggest lower increased risks of breast cancer associated with longer term HRT use, and a more noticeable decline in risks once treatment is stopped, compared with the previous meta-analysis.

No increased risk was found with the use of vaginal estrogen, and there was no evidence of the dose of estrogen used affecting risk.

The study found that the level of increased breast cancer risk associated with HRT depends on a number of factors, which may be able to be reduced by careful choice of treatment, such as the type of progestogen used when it is required for protection of stimulation of the womb lining by estrogen.

This could be of particular benefit to women in their 70s, for whom the levels of increased risk are highest. Many women, however, may be reassured by the low levels of associated increased risk of breast cancer for them from the treatment they are using, according to Dr Vinogradova.

“These results provide clearer, more detailed, and more robust information for doctors and patients about the relative increases in risk of breast cancer for all HRT treatments used in the UK. They should both facilitate and increase confidence in treatment choices, and be useful in the development of best-practice guidelines,” she added.

As always, any associated risks of HRT must be balanced against the benefits and the balance is different for each women. However, for the majority of women under age 60 with troublesome menopausal symptoms, or risk factors for osteoporosis, and for many over that age, the benefits outweigh the risks.