Breast cancer: risk factors

Breast cancer: risk factors2018-08-29T16:27:51+00:00

Breast cancer is the most commonly occurring female cancer in developed countries but earlier diagnosis and improvements in treatment are resulting in the majority of women surviving their diagnosis. In the UK breast cancer survival has improved significantly (by about 40%) over the last 40 years. In the UK in 2014, whilst 54,833 women were diagnosed with breast cancer, 11,360 died from their disease. Eight in ten women diagnosed and treated for breast cancer today in the UK are predicted to survive their cancer for at least ten years.

At present, knowledge of all the factors resulting in the development and growth of breast cancer is incomplete. Gene mutations in breast cells are necessary for all breast cancers to be initiated but progression and further development also depends on complex interactions with lifestyle and reproductive risk factors. Most women diagnosed with breast cancer (about 90%) are considered to be at population risk. The gene mutations resulting in their diagnosis develop during their lifetime. This contrasts with the small proportion of women at high risk due to a strong family history, where the gene mutations are inherited.

Lifestyle and reproductive risk factors associated with an increased risk of breast cancer are summarised below. Most women at population risk have no known risk factors other than growing older and most women who have been exposed to any of these risk factors are never diagnosed with breast cancer in their lifetime.

Factors associated with an increased breast cancer risk include:

  • Increasing age (most breast cancers are diagnosed in women over 50)
  • Family history (approximately 2% of cancers diagnosed annually are attributed to a high-risk inherited gene mutation)
  • ‘High risk’ benign breast conditions
  • Endogenous sex hormone exposure (i.e. prolonged exposure to sex hormone [oestrogen] produced within the body)
  • Early age at starting menstrual periods and late age at menopause
  • Being overweight / obese and post-menopausal
  • Exogenous hormone exposure (i.e. exposure to sex hormones [oestrogen and progestogen] taken in the form of medication)
    • Use of hormonal contraceptives
    • Use of hormones replacement therapy (HRT)
  • Changes to metabolism of female sex hormones
    • Smoking
    • Alcohol
  • Factors increasing the risk of normal breast cells becoming malignant
    • Not having children or a first full-term pregnancy at a later age
    • Not breast-feeding
  • Lack of physical activity

Increasing Age

In the UK, the lifetime risk of being diagnosed with breast cancer for women is 1 in 8. However, this means that 7 in 8 women will never be diagnosed. The risk of diagnosis increases with increasing age and most breast cancers (over 80%) are diagnosed in women aged over 50. In women aged less than 30, breast cancer is diagnosed in about 1 in 1900 women, where this increased to 1 in 15 for women by the age of 70 years.

Family History

This refers to the risk of inheriting a gene mutation that can result in the development of breast cancer. However, only a minority of gene mutations resulting in the development of breast cancer are inherited (i.e. familial breast cancer). Inherited breast cancers account for about 2% of breast cancers diagnosed annually in the UK. Inherited breast cancers are more likely to be diagnosed at a younger age (i.e. less than 40 years), affect both breasts and affect more than one relative within a family. In some families, there is clustering of breast with ovarian, endometrial and bowel cancers. If a woman has a single first degree relative (i.e. mother or sister) or second degree relative (i.e. aunt) diagnosed with breast cancer over the age of 40 it is very unlikely that this places her at an increased risk of breast cancer and she will be considered to be at population risk. There is no need to refer for further risk assessment.

For any woman who has a family history of cancer, discussion with her GP should determine whether this is likely to be significant. The GP should take a family history (national guidance from NICE provides advice to GPs about this). If the family history suggests a woman may be at increased risk (I.e. greater than the general population for her age), the GP will refer to either the local breast unit or local risk assessment clinic as appropriate, where more detailed assessment will take place including whether there is any indication for gene testing and advice about surveillance and possible prevention strategies.

Most women with a family history will not be diagnosed breast cancer in their lifetime.

Benign Breast Conditions

Benign breast conditions refer to a wide range of conditions of the breast. They are categorized according to whether they are associated with an increased risk of being diagnosed with a breast cancer later in life or not. Most benign breast conditions are not associated with an increased risk of diagnosis (this includes for example breast cysts and fibroadenomas).

A ‘high risk’ benign condition refers to the finding in a breast biopsy of either (1) atypical (i.e. abnormal appearing) breast cells or (2) Lobular carcinoma in situ (LCIS) cells. Both are currently considered to be a marker of future risk (this is equal in both breasts) rather than precursor lesions and therefore managed by annual surveillance mammograms for 5 years. Most women with a diagnosis of atypia or LCIS will never be diagnosed with breast cancer in their lifetime.

Endogenous sex hormone exposure

Endogenous sex hormones are produced naturally within the body and refers to the female sex hormones, oestrogen and progesterone. In pre-menopausal women, these are produced by eggs released monthly from the ovaries. In post-menopausal women, the main source of oestrogen production is in fat cells. Female sex hormones have an important but incompletely understood role in the development of most breast cancers. Breast cancer is a condition that predominantly affects women, being 200 times more common than in men. The evidence implicating female sex hormones has largely been drawn from population studies that have revealed an increased risk of breast cancer diagnosis in women who commence their menstrual periods at a younger age or who develop the menopause at an older age (either can result in a longer time of ovarian activity).

  • An earlier age at menarche (onset of periods) is associated with an increased risk of breast cancer diagnosis later in life
  • An earlier age at menopause is associated with a reduced risk of diagnosis of breast cancer.
  • Breast-feeding may reduce the risk of breast cancer as the ovaries do not produce eggs when women breast-feed

In post-menopausal women, ovarian production of oestrogen and progesterone ceases. Small amounts of oestrogen are produced in fat cells, however, by the action of an enzyme called aromatase.

Postmenopausal women who are overweight are at an increased risk of breast cancer and this has been attributed to the fact that there is more fat tissue in which this synthesis of oestrogen can take place.

Exogenous hormone exposure

This refers to sex hormones, which originate outside the body and includes all hormonal contraception (birth control) and hormone replacement therapy (HRT).

1. Hormonal contraception

There is a very small increased risk of breast cancer diagnosis associated with hormonal contraceptives but for most women at population risk, the benefit in reducing un-intended pregnancy and the risk of diagnosis of other cancers (i.e. ovary, endometrium) outweighs this potential concern. Overwhelmingly, clinical studies that have looked at the question of breast cancer risk are restricted to women who have used the combined oral contraceptive pill (i.e. containing oestrogen with a progesterone) and were conducted many years ago on preparations that are no longer in clinical use, which tended to contain higher dosages of sex hormones. There is a lack of information about the progestogen-only pill, progestogen implants, injectable progestin, inter-uterine progesterone [the Mirena Device]) and no clinical studies have yet reported on risk with combined vaginal or transdermal preparations. If with any of these the risk of diagnosis of breast cancer is increased it is likely to be small and similar in degree to that with COCP.

2. Hormone replacement therapy (HRT)

Unopposed HRT (i.e. preparations containing oestrogen alone) is associated with little or no change in risk of breast cancer but combined HRT (i.e. oestrogen with a progestogen) can be associated with a small increased risk. Any increase in risk is related to treatment duration and reduces after stopping HRT. The risk of breast cancer with combined HRT is less than that associated with being overweight over the age of 50 or that associated with drinking 2 or more units of alcohol per day. – See our related factsheet on HRT: What you should know about the risks and benefits. For women experiencing hot flushes and night sweats, with a low underlying risk of breast cancer (i.e. most of the population) the benefits of HRT in the short-term (up to 5 years’ use) will exceed any potential harm. There is no evidence the risk of dying from breast cancer is increased in women with a history of using it.

Smoking

Clinical studies have shown smoking does increase the risk of breast cancer diagnosis in current and former smokers. This risk appears to be increased particularly in teenagers who start to smoke prior to their first pregnancy. There is no clear evidence as to whether risk is affected by the duration or amount of smoking.

Alcohol

Alcohol consumption is associated with an increased risk of breast cancer diagnosis. Risk does not persist in past users of alcohol. Currently it is unclear whether there is a ‘threshold’ below which risk is not increased.

Factors increasing the risk of normal breast cells becoming malignant

In women who have never had a pregnancy, of had a full-term pregnancy later in life or never breast-fed, the cells in the breast are less resistant to the effects of carcinogens (substances initiating malignant change in cells). Part of the reason women in developed countries have a higher risk of breast cancer diagnosis than women in developing countries may be due to the former having fewer children and avoiding or limiting the duration of breast feeding.

The risk of breast cancer diagnosis is decreased:

  • In women who have their first full-term pregnancy at a younger age
  • In women who have more than one full-term pregnancy
  • In women who breast-feed (this protection may be restricted to the risk of diagnosis of breast cancer in pre-menopausal women)

Physical Activity

About 3% of breast cancers diagnosed in the UK are attributed to lack of physical activity. Clinical studies suggest that increasing physical activity may only be protective and reduce the risk of breast cancer diagnosis in post-menopausal women. Evidence is unclear as to the level of physical activity that could be protective and how increasing physical activity confers this protection. It may in part be related to weight reduction.

Breast Cancer Management

Annually in the UK about one quarter of breast cancers are diagnosed via the NHS Breast Screening Programme (NHSBSP). The remainder are diagnosed in women (and some men) who present to their GP with breast symptoms. For information on breast screening and self-examination, look at the factsheet ‘Breast Care and Self-examination’.

Currently, with optimal treatment 2 in 3 women will survive their disease beyond 20 years. For many women, it is a condition they live with, rather than die from. Female deaths from breast cancer per year in England and Wales (4%) are much lower than those due to Alzheimer’s disease and dementia (16%), heart disease (8%) and stroke (7%). Once a diagnosis of breast cancer is confirmed, management generally involves varying combinations of the following treatments (e.g. surgery, radiotherapy, anti-oestrogen hormone therapy, chemotherapy and immunotherapy such as herceptin). Treatment recommendations are based on the individual features of a breast cancer (e.g. the size, grade and stage of the breast cancer) sometimes, menopausal status and an individual’s general health.

Useful contacts

Breast Cancer Now

5th Floor Ibex House, 42-47 Minories, London, EC3N 1DY
222 Leith Walk, Edinburgh, EH6 5EQ
Supporter Engagement team on 0333 20 70 300
Website: www.breastcancernow.org

Breast Cancer Care

Tel: 020 7384 2984
Helpline: 0808 800 6000 Mon-Fri 9am-5pm, or Sat 9am-2pm
Email: info@breastcancercare.org.uk
Website: www.breastcancercare.org.uk

National Institue for Clinical Excellence (NICE)

Website: www.nice.org.uk
Familial Breast Cancer Guidance
Early and Locally Advanced Breast Cancer Guidance

Menopause: Giving you confidence for understanding and action

Topics in the series include:

Risk of breast cancer diagnosis associated with lifestyle and reproductive risk factors
Absolute risk of diagnosis per 1000 women aged 45 to 79 (baseline risk 23/1000 over 7.5 years)
Number of cancers diagnosedNumber of cancers not diagnosedExcess risk
No exposure12988
Risk increased:
Postmenopausal obesity or overweight27-40960-973+4 to +17
Never having given birth39961+16
Late age at first live birth (31 years or older)31969+8
Alcohol (regularly drink two units or more per day)29971+6
Combined hormonal contraceptives29971+6
Combined HRT29971+6
Smoking (current smoker)26974+3
Risk reduced:
Having your first period at 15 or older19981-4
Estrogen only Hormone Replacement Therapy (HRT)17983-6
Giving birth to 4 or more babies15985-8
Taking at least 30 minutes moderate exercise five times per week13987-10

This factsheet has been produced by Women’s Health Concern and reviewed by members of our Medical Advisory Panel. It is for your information and advice and should be used in consultation with your own medical practitioner.

Reviewed: December 2017

Next review due: December 2019

Women’s Health Concern is the patient arm of the British Menopause Society

Registered Charity No. 279651

Website: www.womens-health-concern.org