Breast cancer is the most common cancer in women worldwide, with nearly 1.7 million new cases diagnosed in 2012 (second most common cancer overall). This represents about 12% of all new cancer cases and 25% of all cancers in women. It is the fifth most common cause of death from cancer in women.
Breast cancer risk doubles each decade until menopause, after which the increase slows. However, breast cancer is more common after menopause. Survival rates for breast cancer vary worldwide, but in general rates have improved. This is because breast cancer is diagnosed at an earlier and localised stage in nations where populations have access to medical care, and progressive improvement in treatment strategies. In many countries with advanced medical care, the five-year survival rate of early stage breast cancers is 80–90 per cent, falling to 24 per cent for breast cancers diagnosed at a more advanced stage.
Most breast cancer subtypes are hormone-related. The natural history of the disease differs between those diagnosed before and after the menopause, which may be due to different kinds of tumour and possibly different effects of nutritional factors on hormones depending on menopausal status.
Life events are important risk factors for breast cancer including 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, as they 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. Ionising radiation exposure from medical treatment such as X-rays, particularly during puberty, increases the risk of breast cancer, even at low doses. Hormone therapy (containing oestrogen with or without progesterone) increases 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.
The Continuous Update Project Panel judged that for premenopausal breast cancer there was strong evidence that consumption of alcoholic drinks, greater birthweight and adult attained height are causes of premenopausal breast cancer. The panel also judged that there is strong evidence that vigorous physical activity and greater body fatness protect against premenopausal breast cancer.
The Panel judged that for postmenopausal breast cancer there was strong evidence that consumption of alcoholic drinks, greater body fatness throughout adulthood, adult weight gain and adult attained height are causes of postmenopausal breast cancer. The Panel also judged there is strong evidence that physical activity (including vigorous physical activity) and greater body fatness in young adulthood protect against postmenopausal breast cancer.
In addition, the Panel judged there was strong evidence that lactation protects against breast cancer (unspecified menopausal status).
Preventability estimates show that about 22% of cases of breast cancer in Brazil can be prevented by not drinking alcohol, being physically active and maintaining a healthy weight.
The countries with the top 20 highest incidence of breast cancer in 2012 are given in the table below.
|Rank||Country||Age-Standardised Rate per 100,000 (World)|
|9||United States of America||92.9|
The top 20 countries with the most breast cancer survivors are provided in the table below. The statistics are for 2012 and show the number of breast cancer survivors who were alive five years after diagnosis. The order in which the countries are ranked is based on the number of breast cancer survivors per 100,000 adult women in each country.
|Rank||Country||Number of women still alive five years after a breast cancer diagnosis|
|9||United States of America||970,693|
Source: Ferlay J, Soerjomataram I, Ervik M, Dikshit R, Eser S, Mathers C, Rebelo M, Parkin DM, Forman D, Bray, F. GLOBOCAN 2012 v1.1, Cancer Incidence and Mortality Worldwide: IARC CancerBase No. 11 [Internet]. Lyon, France: International Agency for Research on Cancer; 2014. Available from: http://globocan.iarc.fr, accessed on 16/01/2015.