The risk of breast cancer increases with age in both developed and developing countries. For the population as a whole, malignancies rarely occur before the age of 25, and the rate of prevention of breast cancer increases significantly after the age of 40. Some data suggest that breast cancer screening for women over the age of 40 has the potential to reduce breast cancer mortality. Principles of breast cancer screening: 1. 18-39 years old: monthly breast self-examination and 3-yearly clinical checkup. 2. 40-49 years old: 1 clinical physical examination and mammogram every year. Women at high risk should consult with their doctors about the need to start screening before the age of 40 and the interval between mammograms at the age of 40-49. 3.Over 50 years old: 1 clinical checkup and mammogram every year and 1 breast self-examination every month.