Screening for breast cancer.

There is very good evidence that screening for breast cancer reduces mortality in women older than 50 years and suggestive but inconsistent evidence that screening is effective in reducing long-term mortality in women younger than 50 years. The probability that an average-risk woman will be diagnosed with breast cancer in the coming 10 years is about 130 in 10,000 for a 40-year-old woman, 230 in 10,000 for a 55-year-old woman, and 280 in 10,000 for a 65-year-old woman. The chance of dying from breast cancer diagnosed in the coming 10 years is about 90 in 10,000, 123 in 10,000, and 120 in 10,000 for women age 40, 55, and 65, respectively. Mathematical models based on data from controlled trials of screening programs indicate that screening annually for 10 years with breast physical examination will decrease the probability of death from breast cancer by about 25 in 10,000 for women in the three age groups and increase life expectancy by about 20 days. Adding annual mammography will decrease the probability of death from breast cancer an additional 25 in 10,000 and increase life expectancy an additional 20 days. The actual reductions in mortality observed in controlled trials are slightly lower. If women are screened annually for 10 years with breast physical examination and mammography, the chance for a false-positive result over the 10-year period is approximately 2500 in 10,000. On the population level, if 25% of women age 40 to 75 are screened annually with both examinations, deaths from breast cancer would be decreased by about 4000 in the year 2000. Net annual costs would be approximately $1.3 billion. Recommending a screening strategy requires weighing the benefits against the risks and costs.