Is hormone treatment risky and does it increase the risk of breast cancer?

The Women’s Health Initiative (WHI) studies from 2002 and 2004 raised alarm bells regarding MHT usage. Importantly, however, subsequent studies, and improved hormonal formulations, have provided a far better understanding of the risks of MHT. These new studies show that MHT provides more benefits than risks when used within the first 10 years of the menopause and in women under 60.

Some key facts related to MHT:

  • MHT does not increase the risk of breast cancer if used for less than 5 years. There may be a small increase (about 1 extra case per 1000 women) in breast cancer when using combined MHT (oestrogen + progesterone) in tablet form for longer than 5 years.
  • The risk of breast cancer does not appear to be increased if certain types of progesterone are used, like Dydrogesterone and those with an identical structure to the body’s own progesterone (e.g. Prometrium).
  • There is no increased risk of breast cancer for oestrogen-only MHT.
  • Based on the above 3 points, any increased risk for breast cancer related to MHT appears to be due to progesterone usage and not oestrogen.
  • MHT does not increase the number of heart attacks or death from heart disease if taken within 10 years of the menopause. Indeed, oestrogen-only MHT may decrease the risk of heart disease.
  • In women less than 60, MHT used in tablet (oral) form causes a very small increased chance of having a blood clot. This occurs because hormones taken via the mouth pass through the liver after being absorbed by the gut and cause a change in the production of clotting factors in the liver. The absolute risk of having a clot due to MHT remains very small, 1 extra case for every 1000 women on MHT.
  • MHT given via the skin (e.g. patches) bypasses the liver and has not been found to increase clot formation. This is the preferred form of MHT for women with increased risk for clots (e.g. overweight women and smokers). A very large study involving over 450,000 women in the UK was published earlier this year in the British Medical Journal and confirmed that using oestrogen via the skin (e.g. patches and gel) does not increase the risk of blood clots.
  • The risk of blood clots is higher for combination MHT than for oestrogen-only MHT.
  • MHT does not increase the risk of stroke in women under 60 or within the first 10 years of the menopause who do not have risk factors for stroke.
  • MHT is not advisable for women who have had hormone-dependent cancers such as cancers of the breast and womb lining (endometrium).
  • Vaginal oestrogen is the preferred and most effective treatment for GSM symptoms such as vaginal dryness and burning and painful sexual intercourse. A very recent study based on the large US Nurses’ Health Study found that vaginal oestrogen is very safe and does not increase risks for heart attacks, blood clots, strokes or cancers of the womb and breast.

The risks associated with MHT depend on various factors. The key ones are:

  • Age and length of treatment. The safest time is within the first 10 years after menopause and for women under 60.
  • Other co-existing conditions. Risks are increased in women who are obese, who smoke and who have had other medical conditions such as clots in the veins or an inherited tendency to form clots.
  • Whether progesterone treatment is also required. Some risks associated with MHT (e.g. breast cancer, heart disease and clots in the veins) are more strongly related to the progesterone component.
  • Risks associated with progesterone may be minimised by:
    • Using body-identical progesterone (see below)
    • Delivering progesterone directly to the womb lining instead of through the blood by means of a progesterone-releasing device placed inside the womb (Mirena)
    • Using a type of medication called a Selective Estrogen Receptor Modulator (SERM) instead of progesterone to protect the womb lining from oestrogen. One preparation known as DuaviveTM contains the SERM, Bazedoxifene, in combination with conjugated oestrogen.
  • The method of administering MHT. Treatments given via the skin (e.g. patches) or the vagina are not associated with the increased risk of clot formation seen with MHT in tablet form. As mentioned above, earlier this year, a very large UK-based study confirmed that oestrogen given via the skin does not increase the formation of blood clots. A very recent study conducted in the USA found that vaginal oestrogen was very safe and did not increase risks for heart attacks, blood clots, strokes or cancers of the womb and breast.
  • The structure of the hormones used. Some hormones are identical in structure to those found in the body. These hormones are known as body-identical. Body-identical hormones may be safer than other types of hormones that have different structures.
    • Body-identical oestrogen (e.g. 17β-Oestradiol) is available as tablets, patches, gels and vaginal treatments. A recent large study conducted in the UK found that oestrogen in the form of oestradiol is less risky in terms of clot formation compared with conjugated equine oestrogen.
    • Body-identical progesterone is available as capsules (Prometrium) that can be used orally or vaginally.