There is a growing number of patients who have not had children before the diagnosis of breast cancer, or have the need to have a second child after treatment. This need is even more evident in the “second child era” when the policy allows. However, breast cancer is a systemic and systemic disease, and various treatments for breast cancer may affect the fertility of patients. Does breast cancer treatment during pregnancy affect the mother and fetus? Should breast cancer patients terminate their pregnancy or not? Fertility or survival is a difficult question. There is not much research on the relationship between breast cancer and pregnancy in China. However, the findings of some foreign guidelines and clinical studies are available for our reference. The Royal College of Obstetricians and Gynecologists (RCOG) updated the Guidelines on Breast Cancer and Pregnancy in 2011. The sources of evidence for the guidelines are Medline, Pubmed, all EBM reviews, randomized controlled trials in EMBASE and TRIP, systematic reviews, meta-analyses, cohort studies, and case-control studies. 12 recommendations from experts: 1. Although amenorrhea after endocrine therapy improves the prognosis of hormone receptor-positive patients, studies have shown that post-treatment fertility does not affect the long-term survival of breast cancer patients and can even reduce the relative risk of death in patients. 2. Some studies suggest that there is no statistically significant difference in the incidence of genetic abnormalities and childhood-onset tumors in offspring born to cancer patients compared to the general population. 3. Chemotherapy and endocrine therapy are detrimental to ovarian function in women, but due to the hormone-dependent nature of some breast cancers, the impairment of ovarian function partially plays the role of endocrine therapy. Some patients may stop menstruation or even lose their fertility after the end of combined treatment. Therefore, if, after the diagnosis of breast cancer, the patient still has plans to have children, he or she must inform the competent doctor about the use of ovarian protection before resorting to chemotherapy and endocrine therapy. Ovarian protection can be achieved with drugs such as goserelin and leuprolide (although these drugs do not protect fertility in 100% of patients), which need to be started about 2 weeks before systemic treatment. There is also recourse to assisted reproductive technology (this requires consultation at a fertility center). 4. An international study published online August 16 in The Lancet Oncology concluded that women with breast cancer can be treated during pregnancy without an increased risk of adverse fetal and maternal outcomes. However, the researchers did find that fetuses exposed to chemotherapy in utero had lower birth weights and more complications than unexposed fetuses, but there were no significant differences between the two groups. Importantly, there were no major birth defects. However, given the medical practices in the country, most mammologists would not advise their patients to go for pregnancy during chemotherapy and endocrine therapy. Especially in the first trimester of pregnancy, these oncology drugs are more likely to cause fetal abnormalities. Patients taking tamoxifen are advised to stop taking the drug for at least 3 months before considering pregnancy. 5. Breast cancer patients should consult their mammologists and obstetricians and gynecologists before getting pregnant. Before preparing for pregnancy, some routine examinations should be done to rule out tumor recurrence and metastasis. 6.Patients with metastatic breast cancer who have been diagnosed with advanced stage (stage 4) are no longer recommended to get pregnant. 7.For patients with intraductal carcinoma and lobular carcinoma in situ, there is not much evidence, and my personal opinion is that you can go for pregnancy with more confidence. 8.As for how long after the diagnosis of breast cancer before pregnancy, it is generally recommended at least 3 years later. This is because most of the recurrence and metastasis of breast cancer occurs within 3 years after diagnosis. 9. Previous evidence suggesting that pregnancy does not increase the recurrence of breast cancer is after the completion of breast cancer treatment. Therefore, some patients ask if they interrupt their normal treatment for breast cancer, get pregnant and have a baby, and then supplement the treatment later. I have not found any information on whether this will increase recurrence. 10. Since chemotherapy and molecular targeted therapy may affect the heart function, pregnancy may also increase the heart and lung burden. Echocardiography should be emphasized during pregnancy. 11.Bone scan and pelvic x-ray are not recommended during pregnancy. 12.Can I breastfeed after breast cancer surgery? At present, breastfeeding is considered possible on the healthy side of the breast. For patients with breast-conserving surgery, many patients lose the breastfeeding function on the affected side due to the fibrosis of the tissue after radiotherapy. Breastfeeding is not recommended for patients who are taking tamoxifen or using Herceptin.