We know that among white women, about 25% of breast cancer patients are <50 years old and 6% <40 years old, and that in recent decades, breast cancer is becoming increasingly young as a trend in breast cancer incidence. In China, this trend is even more pronounced. And among these younger patients, many still have reproductive needs. Therefore, reproductive health issues, including fertility after breast cancer (including related treatment) and pregnancy, are extremely important for those with reproductive needs, but many questions about the safety of pregnancy in this group of patients have not been answered. In 2011, Breast Cancer International (BIG) and the North American Breast Cancer Group (NABCG) discussed the complex issues of fertility and pregnancy in women with a history of breast cancer in a question-and-answer format regarding reproductive issues, including fertility, pregnancy, contraception, and menopause (Breast Cancer Res Treat (2011) 129:309C317). We have translated the article and reorganized it for the benefit of patients in need. Do young breast cancer patients have the desire to become pregnant? Since 1991, there has been a global trend of increasing pregnancy rates among women >30 years of age for a variety of reasons (e.g., culture, education level, occupation). In the United States, the percentage of first-time mothers at >30 years of age has increased from 4.1% to 21.2% since the 1990s. Thus, this means that more and more women may face the problem of developing breast cancer before completing their childbearing plans. Data from retrospective studies clearly show that many “young” breast cancer patients are significantly concerned about whether subsequent treatment will result in infertility when breast cancer is diagnosed. For patients <35 years of age with early-stage breast cancer, Breast Cancer International (BIG) evaluated their attitudes about the risk of loss of fertility due to follow-up treatment, and the results will be published. "In a study of young women with breast cancer by Help Yourself, Help Others (HOHO), more than 50% of women ≤40 years of age were found to be concerned about future fertility, and a high percentage had the intention to consider pregnancy after breast cancer treatment. Does pregnancy after breast cancer affect recurrence? This question is a major concern for many clinicians and patients. In the past, pregnancy in breast cancer patients was considered to be a risk factor that increased the potential for recurrence. The rationale was that during pregnancy, elevated estrogen and progesterone, pituitary prolactin, and placental prolactin can adversely affect the underlying tumor tissue, and this was the primary reason why breast cancer patients were advised not to become pregnant in the past. However, recent research evidence suggests that rather than increasing the risk of recurrence, pregnancy after breast cancer may in fact have a protective effect. In several retrospective population-based studies, using age, stage of disease, and year of diagnosis as a pair, women who became pregnant after breast cancer were found to have a lower risk of death-related outcomes than patients who did not become pregnant. In two of these studies, survival rates were even higher for those who became pregnant than those who did not, and these findings support pregnancy in breast cancer patients. A recent meta-analysis analyzed 14 similar studies, including 1244 pregnancy cases and 18,145 control cases. The analysis showed that patients who became pregnant had a 41% reduced risk of death compared to those who did not become pregnant after breast cancer. One possibility in such an unexpected analysis is the selection bias of the researchers, also known as the "healthy mother" effect, such that most researchers selected breast cancer patients with a good prognosis to be advised to become pregnant and included in the study group, while this group of patients was the "healthier" patients. For example, most researchers select patients with good prognosis for breast cancer to be advised to become pregnant and included in the study group, and these patients are "healthier" patients. In vitro preclinical data also suggest that in endocrine-sensitive breast cancer cells, high levels of estrogen and progesterone induce apoptosis and that human chorionic gonadotropin (HCG) levels are similar to those of patients studied during pregnancy. In addition, the fetal antigen hypothesis suggests that maternal immunity will be enhanced during pregnancy, which in turn fights breast cancer cells. However, data from prospective studies are needed to determine the true effect of pregnancy on the prognostic impact of breast cancer. Recent data support that pregnancy is safe even in carriers of the breast cancer genes BRCA1 and BRCA2. Therefore, with adequate genetic counseling and adequate psychological support, pregnancy should not be discouraged in breast cancer patients. Despite the growing evidence in favor of pregnancy, the number of patients who become pregnant and deliver successfully after breast cancer remains low (3-15%, depending on the age of the patient). This low probability may be attributed to a variety of different factors (e.g. treatment-induced infertility, resistance, recurrence concerns, inadequate counseling, and patient wishes). The provision of evidence-based information and psychosocial support for breast cancer patients who wish to become pregnant is an important area for improvement. Can adjuvant therapy jeopardize ovarian function? Data on the incidence of chemotherapy-induced amenorrhea (CIA) are too contradictory, mainly because there is no standardized definition of amenorrhea in different studies, a wide range of time points for assessing amenorrhea, and inconsistent age group segmentation fields. On the other hand, it is well known that ovarian aging, i.e., follicle number and quality, declines at an accelerated rate around 35 years of age, with oocytes declining to close to 25,000 (close to 300,000 at puberty). Overall, the actual risk of ovarian failure after chemotherapy may be underestimated because the incidence of amenorrhea is usually used in studies as a proxy for the rate of fertility loss. The most commonly used adjuvant chemotherapy regimens include agents that are commonly used and have a negative impact on fertility; the rate of permanent menopause depends on the agent used and the total dose, as well as the age of the patient at the time of treatment. Alkylating agents, in particular, are highly toxic to the primordial follicle, which represents the reserve of the ovary. Overall, amenorrhea rates are significantly higher after chemotherapy in patients ≥40 years of age, although many studies did not analyze them stratified by age. There are also limited data for women younger than 35 years, and some data suggest that the probability of chemotherapeutic amenorrhea (CIA) in this age group is extremely low (0-10% in most studies). Although breast cancer is rare in this age group, exact data are very useful because these women are most likely not to have had children. Transient irregular periods or amenorrhea are common with chemotherapy, but a certain percentage of patients resume menstruation within 6-12 months of completing treatment, a time that coincides with the replacement of damaged developing follicles by new follicles from the remaining primordial follicular pool. Furthermore, it is worth noting that even if women continue or return to menstruation, their fertility is often impaired and they may experience early menopause due to the loss of a significant percentage of the primordial follicular pool. Since the number of young patients who do not undergo adjuvant chemotherapy is small, it is difficult to know how the tamoxifen used after chemotherapy affects ovarian function. In therapeutic amenorrhea, the effect of tamoxifen is controversial: some studies demonstrate that the addition of tamoxifen increases the incidence of amenorrhea, while others report no effect. In young women, the effect of tamoxifen on amenorrhea is minimal. Although scattered X-rays during radiation therapy can reach the pelvis and ovaries, standard adjuvant radiation therapy for breast cancer does not cause significant ovarian toxicity. Is adjuvant therapy harmful to the fetus? One of the main concerns of patients is the potential teratogenic effects of breast cancer treatment on future pregnancies. There are few available data on the outcome of births in breast cancer patients: in general, there are no reports of health risks for offspring of breast cancer patients that exceed those of the normal population. In all articles, including the 5,752 patients in the Breast Cancer Cooperative Group trial and the Case-Control Study study, the abortion rate was very high (20-44%), possibly reflecting patient and physician concerns about the safety of pregnancy after breast cancer. More recently, two large population-based cohort studies have shown that adverse births are not higher in breast cancer patients than in healthy populations. However, in the Swedish cohort study, breast cancer patients had an increased risk of delivery complications, cesarean section, preterm delivery (<32 weeks), and low birth weight (<1500 g) compared to healthy controls.