A study published by the BMJ provides new estimates of the increased risk of breast cancer (BCa) associated with use of different hormone replacement therapy (HRT) preparations in the UK.
The research, carried out by a team at the Universities of Nottingham and Oxford, assessed the differences in risk of BCa associated with the individual component hormones used in HRT, using data from QResearch and CPRD. The data was linked to hospital records to compare HRT prescriptions for 98,611 women aged 50-79 diagnosed with BCa between 1998 and 2018, with those of 457,498 women of the same age and from the same general practice who did not develop breast cancer.
Overall, 33,703 (34%) women with a diagnosis of BCa and 134,391 (31%) controls had used HRT recently or in the past.
Risk increases were mostly associated with oestrogen-progestogen treatments, but small increases were also associated with oestrogen-only treatments.
For recent long-term users, compared with never use, there was a 15% associated increased risk of developing BCa for oestrogen-only therapy, while there was a 79% associated increased risk for combined oestrogen and progestogen therapy.
Past long-term use of oestrogen-only therapy and past short-term use of oestrogen-progestogen formulas were not associated with increased risk. The risk associated with past long-term oestrogen-progestogen use, however, remained increased (16%).
Therefore, in recent oestrogen-only users, 3-8 extra cases per 10,000 women years would be expected, depending on age. In oestrogen-progestogen users, between nine and 36 extra cases per 10,000 women years would be expected. For past oestrogen-progestogen users, the results would suggest between two and eight extra cases per 10,000 women years.
The combined treatment associated with the lowest risk increase was oestradiol-dydrogesterone.
“Our results add more evidence to the existing knowledge base and should help doctors and women to identify the most appropriate HRT formulation and treatment regimen, and provide more consistently derived information for women’s health experts, healthcare researchers, and treatment policy professionals,” the authors say.