Use of hormone replacement therapy and risk of breast cancer: nested case-control studies using the QResearch and CPRD databases

Study (n=98,611 breast cancer matched to 457,498 controls) presents new generalisable estimates of increased risks of breast cancer with different HRT preparations in UK. Risks varied between types of HRT, with higher risks for combined treatments and longer duration of use.

SPS commentary:

Compared with never use, in recent users (<5 years) with long term use (≥5 years), oestrogen only therapy and combined oestrogen and progestogen therapy were both associated with increased risks of breast cancer (adjusted odds ratio 1.15 [95% CI 1.09 to 1.21] and 1.79 [1.73 to 1.85], respectively). Past long term use of oestrogen only therapy and past short term (<5 years) use of oestrogen-progestogen were not associated with increased risk, but the risk associated with past long term oestrogen-progestogen use remained increased (1.16, 1.11 to 1.21).

British Medical Journal