Breast tissue comprises mainly fat, glandular tissue (arranged in lobes), ducts and connective tissue. Breast tissue develops in response to hormones such as oestrogens, progesterone, insulin and growth factors. The main periods of development are during puberty, pregnancy and lactation. The glandular tissue atrophies after menopause. Breast cancers are almost all carcinomas of the epithelial cells lining the breast ducts (the channels in the breast that carry milk to the nipple). Although breast cancer can occur in men, it is rare (less than 1 per cent of cases) and is not included in this review.

CUP breast cancer reportIn total, this report analysed 119 studies from around the world, comprising more than 12 million women and over 260,000 cases of breast cancer.

Incidence and survival rates

Breast cancer is the most common cancer in women worldwide, with nearly 1.7 million new cases diagnosed in 2012, representing about 25 per cent of all cancers in women. Incidence rates vary widely across the world, from 27 per 100,000 in Middle Africa and Eastern Asia to 92 per 100,000 in Northern America. It is the fifth most common cause of death from cancer in women, with an estimated 522,000 deaths (6.4 per cent of the total). It is also the most frequent cause of cancer death in women from regions characterised by lower indices of development and/or income (14.3 per cent of deaths), and the second most frequent from regions characterised by higher indices of development and/or income (15.4 per cent of deaths), after lung cancer.

Breast cancer risk doubles each decade until the menopause, after which the increase slows. However, breast cancer is more common after the menopause. Studies of women who migrate from areas of low risk to areas of high risk show that they assume the rate in the host country within one or two generations. This shows that environmental factors are important in the development of the disease.

Overall survival rates for breast cancer vary worldwide, but in general they have improved. This is because access to medical care is improving in many nations and the majority of breast cancer cases are diagnosed at an earlier and localised stage. In addition, improved surgery and tailored adjuvant treatment regimens are available. In many countries the five-year survival rate for women diagnosed with Stage I/II (small tumours or limited local spread to nodes under the arm) breast cancer is 80–90 per cent. For stages III/IV (larger tumours or more distant spread beyond the breast or to distant organs), the survival rate falls to 24 per cent. The prevalence of breast cancer. in women per 100,000 is 665 in Western Europe, 745 in North America and 170 in Eastern Asia.

The cancer statistics quoted in the Third Expert Report are from the GLOBOCAN 2012 database. The International Agency for Research on Cancer (IARC) updated these statistics in September 2018, after the publication of the Third Expert Report. For the most recent statistics, please click here.

Lifestyle factors and breast cancer risk

In this report from our Continuous Update Project (CUP) – the world’s largest source of scientific research on cancer prevention and survivorship through diet, nutrition and physical activity – we analyse global research on how certain lifestyle factors affect the risk of developing breast cancer. This webpage forms part of the World Cancer Research Fund/American Institute for Cancer Research Third Expert Report Diet, Nutrition, Physical Activity and Cancer: a Global Perspective.

Findings on premenopausal breast cancer

There is strong evidence that:

There is some evidence that:

  • consuming non-starchy vegetables might decrease the risk of oestrogen-receptor-negative (ER–) breast cancer (unspecified)
  • consuming foods containing carotenoids might decrease the risk of breast cancer (unspecified)
  • consuming dairy products might decrease the risk of premenopausal breast cancer
  • diets high in calcium might decrease the risk of premenopausal breast cancer
  • being physically active might decrease the risk of premenopausal breast cancer

Findings on postmenopausal breast cancer

There is strong evidence that:

There is limited evidence that:

  • consuming non-starchy vegetables might decrease the risk of oestrogen-receptor-negative (ER–) breast cancer (unspecified)
  • consuming foods containing carotenoids might decrease the risk of breast cancer (unspecified)
  • consuming diets high in calcium might decrease the risk of postmenopausal breast cancer

See more graphics in our toolkit.

Other causes of breast cancer

In addition to the findings on diet, nutrition and physical activity outlined above, other established causes of breast cancer include:

  • life events

Early menarche (before the age of 12), late natural menopause (after the age of 55), not bearing children and first pregnancy over the age of 30 all increase lifetime exposure to oestrogen and progesterone and the risk of breast cancer. The reverse also applies: late menarche, early menopause, bearing children and pregnancy before the age of 30 all reduce the risk of breast cancer.

  • radiation

Ionising radiation exposure from medical treatment such as X-rays, particularly during puberty, increases the risk of breast cancer, even at low doses.

  • medication

Hormone therapy, also known as hormone replacement therapy or HRT, (containing oestrogen with or without progesterone) increases the risk of breast cancer, and the risk is greater with combined oestrogen plus progesterone preparations. Oral contraceptives containing both oestrogen and progesterone also cause a small increased risk of breast cancer in young women, among current and recent users only.

Pathogenesis

Breast tissue varies at different stages of life in response to host hormonal status and other environmental influences. It is therefore possible that some risk factors will have different effects at different life stages.

Hormones play an important role in breast cancer progression because they modulate the structure and growth of epithelial tumour cells. Different cancers vary in hormone sensitivity. Breast cancers can be classified by their hormone receptor type; for example, to what extent the cancer cells have receptors for the hormones oestrogen and progesterone, which can affect the growth of the breast cancer cells. Breast cancer cells that have oestrogen receptors are referred to as oestrogen-positive (ER+), while those containing progesterone receptors are called progesterone-positive (PR+) cancers. Hormone-receptor-positive cancers are the most common subtypes of breast cancer, but vary by population (60–90 per cent). They have a relatively better prognosis than hormone-receptor-negative cancers, which are likely to be of higher pathological grade and can be more difficult to treat. Many breast cancers also produce hormones, such as growth factors, that act locally, and these can both stimulate and inhibit the tumour’s growth.

Family history of breast cancer is associated with a higher risk of the disease: women with one first-degree relative with breast cancer have almost twice the risk of women without a family history; and women with more than one first-degree relative have about a three- to four-fold higher risk. Some inherited mutations, particularly in BRCA1, BRCA2 and p53, result in a very high risk of breast cancer. Germline mutations in these genes are infrequent and account for only 2 to 5 per cent of cases. During the carcinogenic process, mutations and epigenetic modifications in oncogenes and tumour suppressor genes may be acquired by cancer cells.

Full references and a summary of the mechanisms underpinning all the findings can be found in the breast cancer report.

How the research was conducted

The global scientific research on diet, nutrition, physical activity and the risk of breast cancer was systematically gathered and analysed, and then independently assessed by a panel of leading international scientists in order to draw conclusions about which of these factors increase or decrease the risk of developing breast cancer.

Published findings in peer-reviewed journals

Selected findings from this report have been published in peer-reviewed journals. Details of the papers and links to the abstract in PubMed are below:

Carbohydrates, glycemic index, glycemic load, and breast cancer risk: a systematic review and dose-response meta-analysis of prospective studies. Schlesinger S, Chan DSM, Vingeliene S, Vieira AR, Abar L, Polemiti E, Stevens CAT, Greenwood DC, Aune D & Norat T. Nutr Rev. 2017 Jun 1;75(6):420-441. Abstract

Dietary compared with blood concentrations of carotenoids and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DS, Vieira AR, Navarro Rosenblatt DA, Vieira R, Greenwood DC, & Norat T. Am J Clin Nutr. 2012; 96(2): 356-73. Abstract

Fruits, vegetables and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DS, Vieira AR, Rosenblatt DA, Vieira R, Greenwood DC, & Norat T. Breast Cancer Res Treat. 2012; 134(2): 479-93. Abstract

Dietary fibre and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DSM, Greenwood DC, Vieira AR, Rosenblatt DAN, Vieira R & Norat T.  Ann Oncol. 2012; 23(6):1394-402. Abstract

This webpage is a summary.

For much more, download the full chapter.