Epidemiology

♦ Commonest female cancer in Europe (200 000 cases per year)

♦ 20% of all malignancies

♦ Incidence is increasing by 1% per year

♦ Rate of increase is increasing especially in low-risk populations

♦ Risk of breast cancer correlates with income per capita

♦ Mortality in Western Europe and USA, 15-25 per 150 000 women

♦ In UK—35 000 new breast cancers diagnosed per year

—14 000 breast cancer deaths per year

♦ Breast cancer deaths in UK is highest in world

♦ In UK, recent decrease in breast cancer mortality by 20%

Several risk factors have been identified by epidemiological studies:

♦ Age: breast cancer is very rare before the age of 20 and rare below 30 years. The incidence of breast cancer doubles every 10 years until the menopause, when the rate of increase slows and in some countries plateaus.

♦ Geography: there is a seven-fold variation in incidence between countries, with low rates in the Far East. Migrants from low-incidence countries assume the risk in the host country within two generations.

♦ Age at menarche and menopause: early menarche and late menopause increase the risk. Ovarian ablation before 35 years reduces the risk of breast cancer by 60%; menopause after the age of 55 years doubles the risk.

♦ Age at first pregnancy: nulliparity and late age at first pregnancy increase the risk. A woman whose first pregnancy is at 30 years has double the risk of breast cancer compared with first pregnancy at <20 years.

♦ Family history: genetic predisposition accounts for around 10% of breast cancers.

♦ Exogenous oestrogens: use of oral contraceptives for >4 years before first pregnancy increases the risk of pre-menopausal breast cancer. The use of unopposed oestrogens in hormone replacement therapy for 10-15 years is associated with an increase in breast cancer. Combined preparations also increase the risk, but the magnitude of effect is uncertain.

♦ Diet: associations have been shown with high dietary fat intake, obesity, and alcohol consumption.

♦ Benign breast disease: previous breast surgery for severe atypical epithelial hyperplasia is associated with a four-fold increase in risk.

♦ Radiation: exposure to ionizing radiation at an early age e.g. treatment of Hodgkin's. Mammographic screening is associated with a decrease in breast cancer deaths but the effects of screening younger women are uncertain.

Male breast cancer is rare (0.7% of all male cancers) with a peak incidence 10 years later than women. It may occur in association with

Klinefelter's syndrome.

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