In recent years, breast cancer has become a malignant tumor with a very high incidence among women at home and abroad, and it shows a trend of youthfulness in China. With the progress of comprehensive treatment of breast cancer, more and more breast cancer patients are cured or in remission, some of them have not yet had children at the time of breast cancer and have the requirement to have children after curing. With the liberalization of the national two-child policy, some young women who have already had children still have the desire to have children again, so let’s talk about the fertility of breast cancer patients. According to the fertility guidelines of the Chinese Anti-Cancer Association Breast Cancer Diagnosis and Treatment Guidelines and Norms (2015 edition): Although there is no evidence that fertility affects the prognosis of breast cancer patients, the risk of disease recurrence and the impact of treatment on offspring must be fully considered when choosing whether to have children and when to have children, and there must be adequate communication with patients. Childbirth may be considered in the following cases: (1) After surgery and radiation therapy for patients with carcinoma in situ of the breast. (2) 2 years after surgery for patients with lymph node negative invasive carcinoma of the breast. (3) 5 years after surgery for patients with lymph node-positive invasive carcinoma of the breast. (4) Patients who require adjuvant endocrine therapy, stop endocrine therapy 3 months before conception [e.g., norethindrone, triamcinolone or other estrogen receptor modulators until the end of breastfeeding after childbirth, and then continue endocrine therapy. Modern evidence-based medical data suggest that pregnancy after breast cancer does not increase the risk of recurrence and may even have a protective effect. Commonly used treatments for breast cancer include surgery, chemotherapy, radiotherapy, endocrine therapy, targeted therapy, etc. Do these common treatments have any effect on the fertility of female patients? Will these treatments affect the fetus? Chemotherapy: Chemotherapy plays a pivotal role in the comprehensive treatment of breast cancer. One of the main concerns of patients is whether chemotherapy drugs for breast cancer have potential teratogenic effects. There have been few studies on the health status of babies born in pregnancy after breast cancer treatment. Overall, the health status of the next generation is no more risky than that of the general population. However, a study of 5,752 post-breast cancer pregnancies by the Breast Cancer Collaborative Group found a high rate of abortions, 20-44%, which may reflect concerns of patients and physicians about the safety of pregnancy after breast cancer. The effect of chemotherapy on mature follicles can lead to reversible menopause, while damage to primordial follicles will result in permanent menopause and premature ovarian failure, leading to infertility. Chemotherapy leading to premature ovarian failure is closely related to the patient’s age, type of drug, dose and duration of treatment. The risk of premature ovarian failure with chemotherapy increases with age; the higher the dose of chemotherapy drugs and the longer the course of treatment, the greater the risk of premature ovarian failure. Gonadotropin-releasing hormone (GnRH), is a hormone secreted by the hypothalamus that acts on the pituitary gland. Already analogues of this hormone are in clinical use. After application in breast cancer patients, it can lead to amenorrhea, and menstruation resumes after stopping the drug, so it is equivalent to “removing the ovaries” with the drug. For young female patients with fertility requirements, the application of these drugs during chemotherapy can protect the ovaries to a certain extent. 2.Radiotherapy: At present, radiotherapy mainly targets the local breast, but some radiation may also affect the ovaries and uterus by changing the muscle and blood flow to the pelvis. The standard dose of radiotherapy for breast cancer can scatter through the body to the pelvic cavity, but it is far less than the amount of radiation that can cause premature ovarian failure or uterine damage. Although it does not cause premature ovarian failure, pregnancy and oocyte acquisition should be avoided during radiotherapy. 3.Endocrine therapy: For patients with ER/PR(+) breast cancer, endocrine therapy for several years can significantly improve the prognosis. Some studies have suggested that the use of tamoxifen increases the risk of premature ovarian failure, while others have suggested that the use of tamoxifen has no effect on reproductive function. Animal studies have shown a risk of fetal malformations and increased incidence of mammary tumors with prolonged tamoxifen exposure, so it is advocated that tamoxifen endocrine therapy should be avoided near and during pregnancy. The use of aromatase inhibitors (letrozole, anastrozole, exemestane, etc., which we commonly use) with GnRHa has better efficacy. Aromatase inhibitors have the effect of stimulating ovulation, and they are widely used in assisted reproductive techniques with tamoxifen to promote ovulation, and there are reports of postmenopausal use of aromatase inhibitors to get pregnant again, but the effect of aromatase inhibitors on pregnancy cannot be proven yet. There is no final and definitive answer regarding the safety of pregnancy after breast cancer. This is a question that the International Breast Cancer Collaborative Group is conducting prospective clinical studies to answer. In conclusion, all I can say is that one can still be fertile and can still get pregnant with breast cancer, but one must be cautious.