Breast cancer is the most common cancer in women, accounting for 32% o
f all newly diagnosed cancers. Demographic characteristics associated
with an increased risk include increasing age, birth in North America
or northern Europe, high socioeconomic status, never having been marri
ed, and, for breast cancer diagnosed after 45 years of age, the white
race. Early age at menarche, late age at menopause, late age at first
full-term pregnancy, and low parity increase risk, while removal of th
e ovaries at an early age is protective. Obesity increases risk in pos
tmenopausal women. Having a first degree relative with breast cancer c
onfers an increased risk, especially if both a mother and a sister hav
e had breast cancer at an early age. Mutations in the BRCA1 and BRCA2
genes are associated with an inherited susceptibility to breast cancer
at an early age. Other markers of increased risk include atypical and
hyperplastic epithelial cells in nipple aspirate fluid, nodular densi
ties on mammogram, and biopsy-confirmed benign proliferative breast di
sease. Little can be done at present to reduce breast cancer risk thro
ugh primary prevention, but secondary prevention by mammographic scree
ning in women of age 50 and older reduces mortality from breast cancer
.