Is it OK to use HRT (hormone replacement therapy) ?
Medically Reviewed by Dr Richard Bennett
Last updated on 19.06.2023
Not infrequently, I have a newly diagnosed breast cancer patient who has been on HRT (Hormone Replacement Therapy). The questions invariably come:
- Did HRT cause my breast cancer?
- Do I need to come off HRT?
What’s the evidence relating to HRT and breast cancer risk for you?
First of all, why do women use HRT–what are the benefits? Well, 80% of women will experience menopausal symptoms, be they hot flushes, drenching sweats, pelvic dryness, sexual dysfunction, mood and/or sleep disturbance. In addition, menopause can be associated with bone thinning and fractures and even increased cardiovascular (heart) risk. HRT can help with all of these – hence it’s popularity, especially before the association with increased breast cancer risk was realised
- The problem is, HRT has a stimulatory effect of breast tissue. Whilst this can mean firmer, more youthful breasts, in an ageing population where breast cancer is inherently more common, this extra stimulatory effect can increase the risk of a cancer mutation in breast cells.
- As an aside, HRT is also associated with an increased risk of blood clots – for example in the calf, lung and even brain (stroke). The risk is similar to that of being a smoker, or using the oral contraceptive pill. Some HRT preparations can predispose to endometrial (womb) cancer and HRT also gives an increased tendency to gallstones.
- Two major studies initiated in the ‘90s have significantly influenced our understanding of HRT and breast cancer. These are the Women’s Health Initiative and the Million Women Study.
Combined HRT (Oestrogen + Progesterone)
- Approximately one in a 1000 women using HRT for an average of five years will develop breast cancer when they otherwise wouldn’t have if they didn’t use HRT* (see below)
- Use under two years probably carries no significant additional risk
- It’s unclear whether HRT use between two and five years duration carries much risk or not
- After ceasing HRT, breast cancer risk returns to normal by five years at latest
Oestrogen only HRT
- Oestrogen only HRT carries no significant increased risk for breast cancer when used for under 10 years, however this is not suitable in women without hysterectomy given the increased risk of uterine (womb) cancer otherwise.
Synthetic steroids with oestrogenic and progestogenic activity
- Prescription medications in this category may carry an increased risk of breast cancer between that of
oestrogen only preparations and combined HRT
“Bioidentical” or “natural” HRT
This is very difficult to study given there’ll be varying ingredients and concentrations between makers – there’s no uniform “recipe”. Realistically,the risks and benefits are likely to be similar to equivalent commercially produced preparations.
Other factors
Similarly, how you take HRT – orally, via skin patches, etc. seems to be irrelevant to risk – although vaginal oestrogen for treatment of atrophy (dryness) doesn’t raise oestrogen blood levels significantly and is not known to increase breast cancer risk. Interestingly, low dose vaginal preparations are probably safe even in breast cancer patients. There’s very little evidence either way about the risks of preparations involving other steroidal hormones such as testosterone.
The British Journal of Cancer contains an interesting paper entitled “Menopausal hormone therapy and breast cancer: what is the true size of the increased risk?” In summary, the authors conclude prior estimations on the risks of HRT and breast cancer might be severely underestimated due to assumptions and inadequate follow up in the source HRT studies. They suggest combined HRT (oestrogen + progesterone) may elevate a woman’s risk of breast cancer by approximately 2.75 x after five years HRT and 3.5 x after ten years HRT. The increased risk at five years HRT use has previously been estimated well below 2 times the risk of those not on HRT.
So what’s the expert advice on HRT?
Cancer Australia’s recommendations suggest weighing up the risk versus benefit of HRT in any given individual. HRT may be a reasonable, ideally short term (less than two to five years) option. Need for ongoing HRT should be re-assessed by the patient and her doctor six to twelve monthly. When HRT required, oestrogen only preparations should be strongly considered in women with prior hysterectomy. HRT in patients with a current or prior breast cancer should be avoided in most cases and should only be entertained in consultation with your doctor, given the increased risk of cancer recurrence.
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