This is the eighth part of our series about the menopause based on our booklet “Fast Facts for Patients: Menopause”, which is freely available online. This article deals with hormone replacement therapy and breast cancer.

Many women are concerned about the risk of being diagnosed with breast cancer if they use hormone replacement therapy (HRT) because research studies have reported conflicting findings, namely that HRT increases, decreases or has no effect on breast cancer risk. This can be very confusing. A major reason for different study results is the different scientific methods used, which can sometimes overly influence positive or negative findings.

Bearing this in mind, current UK advice is as follows.

• Taking oestrogen-only HRT is very unlikely to increase your risk of breast cancer and may even reduce the risk slightly. This is given to women who have had a hysterectomy.
• The risk increases if you are taking combined HRT (oestrogen plus progestogen) but this increased risk only appears to occur in women who have been using combined HRT for a long time (more than 3–4 years). Also, the risk may be less with combined HRT preparations that contain micronised progesterone or dydrogesterone.
• Most women will not be diagnosed with breast cancer if they have previously used HRT (oestrogen-only or combined).
• For women at a low risk of breast cancer (that is, most of the female population), the benefits of using oestrogen-only or combined HRT will exceed potential harms.
• It is useful to think about risk in a balanced fashion. Your risk of being diagnosed with breast cancer is affected by many different things. It may help to know how being overweight and drinking alcohol affect breast cancer risk so that you can see how HRT compares. The table below shows how many additional women would be diagnosed with breast cancer over the next 5 years in a group of 1,000 women aged 50–59 when different risk factors are taken into account. The important thing to note is that the excess risk is small, regardless of the risk factor.

• In women who develop an early menopause, that is, before the age of 50, years of HRT exposure are counted from the age of 50.
• Using certain types of HRT can reduce the risk of bowel cancer, fractures due to osteoporosis (weakened bones) and heart disease.
• Regardless of whether a woman uses oestrogen-only or combined HRT, deaths due to all causes are reduced compared with women who have never used HRT.

Some women are concerned about using HRT because of a family history of breast cancer or a previously diagnosed benign breast condition.

• If you have a family history of breast cancer but have not had breast cancer yourself, talk to your GP. They will ask about your family history and may refer you to a specialist family history clinic or a regional genetics centre (depending on where you live). If you are considered to be at low risk after you have been assessed, you can take HRT.
• The only benign breast conditions associated with a significantly increased risk of a breast cancer diagnosis are epithelial atypia and lobular carcinoma in situ. These two conditions can only be diagnosed if a breast biopsy is performed. HRT should be avoided if you have either of these diagnoses, but HRT is probably without risk for all other benign breast conditions.

Some Breast Cancer Facts

• A woman’s lifetime risk of being diagnosed with breast cancer is 1 in 8. This sounds worrying but it also means that most women (7 in 8) will never be diagnosed with breast cancer in their lifetime.
• The main risk factors for being diagnosed with breast cancer (for most women) are being female and older age. Most breast cancers (~80%) are diagnosed in women over 50 years old.
• Postmenopausal lifestyle factors, such as obesity, high alcohol intake and HRT use, are associated with a small increased risk of breast cancer diagnosis. Most women will not be diagnosed as a result of being overweight, drinking alcohol or using HRT.
• Survival rates for breast cancer have improved significantly over the last 50 years.
• Contrary to popular belief, breast cancer is not the major cause of death in postmenopausal women. The greatest cause of death is Alzheimer’s disease and dementia, followed by heart disease, stroke, chronic lung conditions and influenza or pneumonia.

Please check out the previous and the next post of our series here:

• Menopause: Weighing Up the Benefits and Risks of Hormone Replacement Therapy
• Menopause: Frequently Asked Questions about Hormone Replacement Therapy

Information based on Fast Facts for Patients: Menopause (Karger, 2021).