Breast cancer—epidemiology, risk factors, and genetics

doi:10.1136/bmj.321.7261.624

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Please see: ABC of breast diseases: Breast cancer—epidemiology, risk factors, and genetics

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K McPherson,
C M Steel,
J M Dixon

With 1 million new cases in the world each year, breast cancer is the commonest malignancy in women and comprises 18% of all female cancers. In the United Kingdom, where the age standardised incidence and mortality is the highest in the world, the incidence among women aged 50 approaches two per 1000 women per year, and the disease is the single commonest cause of death among women aged 40-50, accounting for about a fifth of all deaths in this age group. There are more than 14 000 deaths each year, and the incidence is increasing particularly among women aged 50-64, probably because of breast screening in this age group.

Worldwide incidence of cancers in women (1980)

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Worldwide incidence of cancers in women (1980)

Of every 1000 women aged 50, two will recently have had breast cancer diagnosed and about 15 will have had a diagnosis made before the age of 50, giving a prevalence of breast cancer of nearly 2%.

Risk factors for breast cancer

Age

The incidence of breast cancer increases with age, doubling about every 10 years until the menopause, when the rate of increase slows dramatically. Compared with lung cancer, the incidence of breast cancer is higher at younger ages. In some countries there is a flattening of the age-incidence curve after the menopause.

Percentage of all deaths in women attributable to breast cancer

Standardised mortality for breast cancer in different countries

Geographical variation

Age adjusted incidence and mortality for breast cancer varies by up to a factor of five between countries. The difference between Far Eastern and Western countries is diminishing but is still about fivefold. Studies of migrants from Japan to Hawaii show that the rates of breast cancer in migrants assume the rate in the host country within one or two generations, indicating that environmental factors are of greater importance than genetic factors.

Age specific incidence and mortality for …