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The term ‘cancer’ can cause fear and worry but it’s not well understood. At the beginning of the cancer process, cells lose control. They become abnormal and multiply without their usual checks and balances. There are many different types of cancer and these are classified by the type of cell that gave rise to them. The effects of HRT vary for different types of cancers, as you will see below.

This article was included in issue 82 (autumn 2019) of The Menopause Exchange newsletter.

Breast cancer
Breast cancer is the most common female-specific cancer in women. It’s estimated that one in eight women will, at some point in their lifespan, develop this disease. Breast cancer occurs mainly in older women and, with treatment, many live to their natural lifespan. The disease tends to be more aggressive in younger women. In young women in particular, the aim is to diagnose and treat the disease at an early stage to prevent progression.

Scientists don’t believe that breast cancer is caused by hormones. But because breast cancer cells generally still have hormone receptors, these respond in the same way as the original cell type. Oestrogen has a role in cell multiplication, while progesterone has a role in tissue development. When both hormones are present, this will make an existing breast cancer grow more quickly than it would otherwise have done.

In women below the average age of the menopause, adding hormones in the form of HRT has the same effect as if these women were producing their own hormones. Beyond the average age of the menopause, women who naturally continue to have periods will see faster breast cancer growth than those who don’t naturally have periods. Adding HRT causes a similar effect.

It’s estimated that using combined HRT for five years may increase the diagnosis of breast cancer from 12 women in every 1000 women to 15 women. This means there will be an additional three cancers per 1000 women diagnosed at the end of these five years. Confusion lies around whether these are additional cases or simply cases that would have appeared later. The National Institute for Health and Care Excellence (NICE) guidelines in 2015 took the view that no more women would die from breast cancer as a result of taking HRT. The expert view is that the recent report adds little to the information we already had. The report did confirm that the very low dose of oestrogen in vaginal HRT products doesn’t affect breast cancer diagnosis.

The influence of HRT on breast cancer needs to be seen in both context and proportion. The size of HRT’s growth effect on breast cancer is comparable to the effect of drinking two units of alcohol every day. Being obese also increases breast cancer growth; women with a BMI over 30 are at an increased risk of the disease and, for them, taking HRT doesn’t appear to increase this risk further.

Uterine cancer
Uterine cancer arises when the lining thickens without the balancing effect of progesterone. Periods occur because progesterone causes changes in the structure of this lining. When the progesterone levels drop, the lining of the uterus is shed.

Oestrogen on its own stimulates the uterine lining. Without any progesterone being present, there’s a risk that the tissue may become precancerous and ultimately overtly malignant (cancerous). For this reason, women who have any of the tissue that lines the uterus need to have combined HRT (containing oestrogen and progesterone). Continuous combined HRT reduces the risk of endometrial cancer (cancer of the uterine lining) to a lesser degree than if no HRT were used.

Ovarian cancer
Ovarian cancer includes several different cancers and its causes aren’t fully understood. Women who take the combined contraceptive pill to prevent ovulation will find their risk of ovarian cancer is reduced by 50%. This effect lasts for many years after they’ve stopped taking the pill. There’s a degree of confusion surrounding whether HRT makes any difference to ovarian cancer. If there is an effect, it will be very small.

Cervical cancer
Cervical cancer isn’t hormone dependent. Well over 99% of the disease can be attributed to persistent infection with certain human papilloma viruses (HPV). Since 2008, young women have been offered HPV immunisation. In 2019, this will be offered to boys as well. We are just beginning to see a reduction in cervical cancer from the immunisations. Taking HRT makes no difference to this disease. It will, however, make it more comfortable for women to have a screening test, which is important.

Vaginal and vulval cancers
Vaginal cancer is rare. It’s likely to be linked to HPV, but HRT doesn’t seem to play a role. Vulval cancer is a skin cancer and isn’t hormone dependent.

Other cancers
The other type of cancer that’s worth considering is bowel cancer. One of the positive findings of the big study that led to the 2002 HRT scare was that women taking HRT had a lower chance of developing bowel cancer.

So what’s the risk?
The situation is therefore complicated. Cancer depends on the cell it starts from, the tissue and, most importantly, on the woman herself. Many women have been told that HRT causes cancer, but this is misleading. The only cancer that may be caused by HRT is uterine cancer if progesterone isn’t being used as well. Prescribers take great care to ensure this isn’t the case.

Doctors advise women to assess their personal risks for individual cancers. Where lifestyle factors are important, look carefully at what you can do yourself to reduce your risk. Only then should you consider whether HRT is going to increase your personal risk enough to justify not taking it. This will be very rare.

About the author
Dr Sarah Gray is a GP specialist in women’s health at St Erme Medical in Truro, Cornwall.

Created Autumn 2019

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