The influence of hormone therapy on breast cancer risk is uncertain, despite numerous studies focused on this issue. The findings to date suggest the following.
- There is no increased risk of breast cancer from use of oestrogen for up to five years.
- For five to ten years of use a grey area exists, and any increase in breast cancer is probably below 30 per cent.
- For ten years or more of use, there may be a 30 to 80 per cent increase in the risk of breast cancer. This risk appears to be at the higher end of the range in women with a family history of breast cancer (including a mother, sister or daughter affected by the disease) and those using above-average doses of oestrogen.
- It is unclear whether use of a progestogen in combination with oestrogen increases or decreases the risk of breast cancer. Dosages, and hormone types and methods, are not always documented fully in research studies, and this results in unnecessary ambiguity.
- Unanswered questions remain about whether breast cancer risk is increased by the use of oestrogen alone (in women with and without a uterus). There is also debate about whether progestogens teamed with oestrogen are more likely to reduce breast cancer risk if they are taken continuously or for ten to fourteen days a month, as described in chapter 2.
Because of these uncertainties it is very important, if you are on HRT, to be particularly careful to examine your own breasts regularly for any unusual lump or thickening, to have an annual examination of your breasts carried out by your doctor, and to have a mammogram every one to three years. Regular mammograms seem to be a particularly valuable safeguard.