Tamoxifen is a synthetic anti-estrogen drug. The structure is similar to estrogen, which can compete with estradiol for estrogen receptor, form a stable complex with estrogen receptor, and translocate into the nucleus, so that the growth and development of cancer cells are inhibited. The functions of tamoxifen are: 1. Treatment of recurrent metastatic breast cancer and advanced breast cancer in women; 2. Adjuvant treatment for metastasis after breast cancer surgery, prevention of recurrence; 3. Clinical use for functional infertility, functional uterine bleeding, menstrual irregularities, etc.; 4. Endometrial cancer: tamoxifen can increase the level of progesterone receptor effect. If the level of progesterone receptor is low, tamoxifen can be used first to raise the receptor level, and then progesterone can be used for treatment, or both of them can be applied at the same time in order to improve the therapeutic effect.