The causes of breast cancer are still unknown. Epidemiological etiological studies of breast cancer have found that there are many risk factors associated with the development of breast cancer, including: 1. Family history: If a mother, sister, or daughter in the immediate family is a patient, then the chance of the disease in oneself increases 3-5 times. 2. Genetic factors: mutations in breast cancer susceptibility genes (BRCA-1, BRCA-2, etc.). 3, Reproductive factors: age of menarche earlier than 12 years old, age of menopause later than 55 years old, first full-term pregnancy older than 30 years old, not having children, etc. 4.Environmental factors: migration to countries with high incidence of breast cancer, long-term excessive alcohol consumption, long-term excessive intake of high animal fat diet, long-term estrogen replacement therapy, etc. 5. Other factors: postmenopausal obesity, history of atypical breast hyperplasia, etc. How to be screened? 1. 18-39 years old: 1 self-breast examination per month and 1 clinical examination per 3 years. Women with high-risk factors should start breast cancer screening before the age of 40 with doctor’s guidance. 2. 40-49 years old: 1 clinical checkup and mammogram every year. 3.Over 50 years old: 1 clinical checkup and mammogram every year and 1 breast self-examination every month.