Despite the high incidence of breast cancer and the fact that breast cancer in pregnancy is the most common malignancy during pregnancy, the overall incidence of breast cancer in pregnancy remains low, accounting for 0.2% to 3.8% of all breast cancer incidences, half of which are diagnosed during lactation [1]. The incidence of breast cancer during pregnancy in pregnant and lactating women is 1/3000 to 1/10000 [2]. Han Meng, Department of Breast Surgery, Qinhuangdao First Hospital, Qinhuangdao, China There are few reports of this disease and insufficient understanding of its diagnosis and treatment, which need to be summarized to improve the survival rate of the mother and reduce the damage to the fetus. This paper summarizes and evaluates the literature on risk factors, diagnosis, treatment and prognosis of breast cancer in pregnancy. 1. Risk factors for breast cancer during pregnancy: Sex hormones are one of the risk factors for breast cancer, while estrogen, progesterone, and insulin-like growth factor 1 (IGF1) increase significantly during pregnancy, which are closely related to the etiology and progression of breast cancer. The dependence of breast cancer cells on hormones leads to an increased risk of developing breast cancer during pregnancy and has a negative impact on its prognosis. In breast cancer cell cultures and in xenograft models of breast cancer cells, high levels of hormones during pregnancy were seen to increase tumor cell division and tumor volume. Conversely, estrogen receptor blockers and IGF1 signaling blockers inhibit the growth of breast cancer cells in the xenograft model. And is pregnancy itself a risk factor for breast cancer? It is currently believed that there is no significant relationship between pregnancy and breast cancer. Most breast cancers in pregnancy occur in women between the ages of 25 and 40. Assuming an average of 2 pregnancies per woman, 18 months out of 180 months are at risk, which means 10% of the entire course is at risk. Therefore, the consistency of the association between pregnancy and breast cancer is greater than the causality. The clinical manifestations of breast cancer in pregnancy are the same as those of general breast cancer patients: painless lumps in the breast are the main manifestation, but the lumps are usually larger, with the longest diameter of the lumps averaging 4.5 cm, and the lumps in pregnancy are larger than those in postpartum. The median diameter of breast cancer masses in the control group of non-pregnant patients was 2.0 cm. Breast cancer in pregnancy was diagnosed late, with only 7% of pregnant women with palpable breast masses being treated within 1 month and approximately 80% of patients being diagnosed at 12 weeks after delivery. Because of the delayed diagnosis, most patients with breast cancer in pregnancy and lactation have a later clinical stage than non-pregnant patients, and studies have found that women with breast cancer in pregnancy are more likely to be hormone receptor negative and have a higher rate of HER?2 positivity. Patients with diagnosed gestational breast cancer are more likely to be diagnosed in mid to late pregnancy and are older. Several studies have found that the median age at diagnosis of gestational breast cancer is 33-34 years and the median gestation time at diagnosis is 17-25 weeks [13-15]. The majority of tumors are highly differentiated invasive ductal carcinomas with advanced tumor stage. The accuracy of mammography is also related to the experience of the doctor who reads the film. For example, Chen Jiayi et al. reported that 8 out of 9 cases of breast cancer in pregnancy had positive mammography performance. During pregnancy, the mammography dose projected to the fetus is small, with a standard 2 mammograms per breast delivering a dose to the infant of only 0.004 Gy. With protection of the abdomen, the fetus receives a smaller dose. Mammography is safe. On the other hand, ultrasonography is a simple and sensitive test for women who are pregnant and lactating, and it is more sensitive than mammography. Altered hormone levels during pregnancy and lactation cause breast enlargement and follicular hyperplasia, making it difficult to distinguish between hormone-stimulation-induced atypical tissue cell hyperplasia and heterogeneous differentiation of breast cancer by fine needle aspiration biopsy, which can lead to an incorrect diagnosis. Therefore, core needle aspiration tissue biopsy is a more appropriate pathological examination, especially for palpable masses. During pregnancy, traumatic means of consultation of the breast can cause a risk of ductal fistula, with a high risk of bleeding and infection. Discontinuation of breastfeeding before biopsy, prophylactic application of antimicrobials, and attention to hemostasis during biopsy can reduce these risks. In addition during pregnancy, the average dose of radiation to the fetus when CT scans the liver or pelvis is 0.0035 Gy and 0.089 Gy, respectively. therefore, CT is generally not performed in pregnant women, and other imaging tests, such as ultrasound, can be applied to metastases. When MRI is applied and the fetus is exposed to strong magnetic fields, there is a theoretical risk. UKmedicalagency, recommends to avoid MRI in the first 3 months of pregnancy. 3. Treatment progress: Surgery: Surgery is the first treatment for patients with breast cancer. The steps that can be done under local anesthesia are limited, and general anesthesia is mandatory for most patients. In pregnant women, general anesthesia is complicated by its increased blood volume and blood coagulability, decreased lung volume, slowed gastric emptying, and the tendency to postural hypotension from lying supine. A survey of 5,405 of 720,000 pregnant women who underwent surgery found that women who underwent surgery were more likely to deliver low-body-quality babies, caused by immature or delayed intrauterine development. There was an increased neonatal mortality rate, but not an increased rate of congenital malformations or stillbirths. It is difficult to distinguish whether these side effects are caused by surgery, anesthesia, or surgery-related measures. Some reports suggest that breast-conserving surgery, mastectomy and axillary lymph node dissection can be safely performed without such complications. Clinical data on breast cancer in pregnancy are few in number of cases, although prospective and retrospective studies are available. More prospective studies with clinical data are needed to investigate the etiology, diagnosis and treatment of breast cancer in pregnancy in greater depth, ultimately improving the early diagnosis rate, minimizing the damage to the fetus from comprehensive treatment and improving the survival of the mother.