Women who are at increased risk of developing breast cancer may want to consider these medications that may reduce their risk and help prevent cancer. This is less than 5% of women. The main medications to consider are medications known as Selective Estrogen Receptor Modulators (SERMs). They work by blocking the hormone, estrogen, from binding on to breast cells. They are Tamoxifen (which can work in pre- and post-menopausal women), and Raloxifene which has only been tested in postmenopausal women.
There is another type of medication known as Aromatase Inhibitors (AIs) such as anastrozole and exemestane. These reduce the production of estrogen (in tissues other than in the ovaries) but they only work if you are post-menopausal.
The decision to take risk-reducing medication should only be made after a discussion with your medical team about all relevant management options, including screening, and risk-reducing surgery (if appropriate). You need to fully take into account your risk category, age, stage of life and preferences. You and your doctor need to review all the relevant factors to make an informed decision whether risk reducing medication is the way forward for you.
- What are the benefits of breast cancer risk reducing medication?
Both Tamoxifen and Raloxifene reduce the risk of hormone receptor positive invasive breast cancer if taken as a daily tablet for 5 years. Whilst no one can predict what type of breast cancer a woman may develop, the majority of breast cancers women develop are hormone receptor positive breast cancers.
Even though these medications reduce the risk of developing breast cancer (and of needing treatment), we do not know that using them as a risk-reducing medication will actually lead to a longer life. If you have not entered menopause (premenopausal), then Tamoxifen is the only medication that is relevant to consider. If you are in menopause (post-menopausal), then the options also include Raloxifene, or another class of medication, the Aromatase inhibitors (AIs), such as Anastrozole or Exemestane.
- How effective are these medications?
The amount of risk reduction varies from one woman to another. This is because it depends on how much risk you start with. 20mg of tamoxifen or 60mg of raloxifene for five years has been shown in clinical trials to reduce the risk by around 40%. The STAR trial showed that Tamoxifen was slightly more effective than Raloxifene in preventing breast cancer for post-menopausal women (but was not tested in pre-menopausal women).
Tamoxifen use has been shown to reduce the risk of breast cancer for at least 10 years even when taken for five years. It’s not recommended to take for longer than five years. Raloxifene has slightly different side effects (see below), so this needs to be weighed up with a breast specialist, if you are considering one of these medications. The AI medications have not been directly compared to Tamoxifen or Raloxifene. However, when the AI medications were compared to placebo (dummy pills) in trials, a daily tablet of the AI medications reduced risk by about half.
It is still difficult to know if this means that their effect is more than the Tamoxifen/ Raloxifene. The reduction in risk from the AI medications also depends on how high the breast cancer risk was to start with, so it’s good to talk to a doctor who can provide more detailed information to help you decide.
- What are the risks and side effects?
These lists are not exhaustive but are a general guide for each of the medications described.
Tamoxifen – As with any medications, there are risks and possible side-effects. Tamoxifen should not be taken if you’re pregnant or breast-feeding, using the oral contraceptive (Tamoxifen can make this less effective), a smoker (this increases blood clot risk), has had a past history of blood clots in the legs, lungs or a stroke or mini-stroke, or if you are using hormone replacement therapy.
If you’re planning on becoming pregnant in the next few (less than 5) years, then it may be better to think about taking the medication after having children. This is because we do not know if taking the medication for less than 5 years will have a protective effect on breast risk. You should discuss with your doctor if you are using any existing medications and whether these will interact with Tamoxifen.
The most common side effects of Tamoxifen are hot flushes and sweats, especially at night. Sometimes these lessen over the first few months. Possible gynaecological symptoms include vaginal discharge and sometimes, itch, and menstrual irregularities. Each woman’s experience is different, and we cannot predict if a woman will have any of these problems.
Tamoxifen can increase the risk of endometrial (womb) cancer in post-menopausal women (not pre-menopausal women) from about 1 in 1000 women per 5 years to 4 in 1000 women per 5 years of use. This appears to be only for the time the medication is taken. This risk does not appear to apply to Raloxifene and the AI medications.
There is a small increase in risk of blood clots (deep vein blood clots in the legs which can go to the lungs) in pre- and post-menopausal women with Tamoxifen. This is about 4 per 1000 women over five years of Tamoxifen. The risk may be more in women who smoke or have a past history of blood clots. Although the risk of developing blood clots is low (particularly in premenopausal women), this is a serious and potentially life-threatening side effect. The risk of these events returns to normal when Tamoxifen is stopped.
Women may need to stop taking Tamoxifen prior to any surgery. This should be discussed with a healthcare team. It should also be stopped at least three months before trying to start a family.
Raloxifene – Raloxifene should not be used in premenopausal women as it has only been trialled in postmenopausal women. In postmenopausal women, it should be avoided if you’re a smoker (this increases blood clot risk), have had blood clots in the legs, lungs or a stroke or mini-stroke, or if you are using hormone replacement therapy
The most common side effects of Raloxifene are hot flushes and sweats, especially at night. Sometimes these lessen over the first few months. Possible gynaecological symptoms include vaginal discharge and sometimes itch, and menstrual irregularities. Each woman’s experience is different and we cannot predict who will have these symptoms.
There is a small increase in risk of blood clots (deep vein blood clots in the legs which can go to the lungs) in post-menopausal women with Raloxifene. This is about 3 per 1000 women per 5 years of Raloxifene so it is a bit less than with Tamoxifen. The risk may be more in women who smoke or have a past history of blood clots. Although the risk of developing blood clots is relatively low, this is a serious and potentially life-threatening side effect. The extra risk of these events returns to normal when Raloxifene is stopped.
Women may need to stop taking Raloxifene prior to any surgery. This should be discussed with your healthcare team.
Aromatase inhibitor (AI) – These medications such as anastrozole and exemestane should be avoided if a woman could still be premenopausal as they will not be effective. Menopausal status needs to be checked by a doctor before these are considered. AIs should also be avoided if you’re taking hormone replacement (as they will not be effective) or have osteoporosis (as they increase the risk of bone thinning)
The most common side effects of these medications, as with the SERMS, are hot flushes and sweats, especially at night. Sometimes these lessen over the first few months. Possible gynaecological symptoms include vaginal dryness. Each woman’s experience is different and we cannot predict who will have these symptoms, but they do appear to stop when the medications are stopped. Other side effects can include joint aches which vary in severity from one person to another.
The risk of osteoporosis is increased so bone density needs to be monitored while taking these medications by bone density scans (X-rays). Women are advised to take calcium and Vitamin D while on these medications. In contrast, the SERM medications are likely to help with protecting bone density in post-menopausal women.