Pregnancy and lactation breast cancer (PABC) refers to primary breast cancer that occurs during pregnancy or within one year after the end of pregnancy and during lactation, and its incidence accounts for 1.5-8.2% of all breast cancers. It has an insidious onset, rapid progression, and is more malignant than non-pregnant or lactating breast cancer. The histological staging is mostly non-specific invasive breast cancer, especially diffuse invasive type. Because of pregnancy and lactation, the breasts are obviously enlarged and hardened, and the density increases, the smaller cancers are often concealed by the thickened glands and delayed. The following is a retrospective analysis of my treatment of three cases of malignant tumor of breast during pregnancy and lactation. Case 1: Bao××, 26 years old, came to our hospital in June 1999 with a huge lump in her right breast. When the patient was pregnant in June, she found a hard mass of 2 cm in diameter with unclear border and no tenderness in the upper right breast quadrant. After that, the lump continued to increase in size until 2 months after delivery and breastfeeding, when the patient came to our hospital with intolerable swelling and pain in her right breast. On physical examination, the right breast was significantly enlarged about the size of a soccer ball, and the superficial skin veins were angered. After admission, the right mastectomy was performed, and the postoperative pathology was hemangiosarcoma of the breast. Because the tumor was insensitive to radiotherapy, multiple metastases in the liver and lung appeared about three months after surgery, and he died six months after surgery. Case 2: Jiang××, 35 years old, came to our hospital in August 2011 because she was seven months pregnant and found a lump in her right breast for five months. The patient found a peach nut-sized mass in the lower quadrant of her right breast in the second month of pregnancy and visited a local hospital, which was considered as normal glandular thickening during pregnancy and was not further treated by the attending physician. On physical examination, the right breast was about double the size of the contralateral breast, with superficial skin veins angered, a 4-5 cm diameter mass with hard texture and orange peel-like changes in the local skin was palpated in the lower and upper quadrant of the right breast, a large cystic mass was palpated behind the nipple, and multiple enlarged lymph nodes were palpated in the right axilla. After admission, the mass was excised and biopsied as triple-negative moderately differentiated invasive ductal carcinoma, and a modified radical right breast cancer operation was performed. 23/24 lymph nodes in the axilla were metastasized. Case 3: Chen ××, 38 years old, was found to have a 1.5 cm diameter mass in the upper outer quadrant of the left breast during a routine pregnancy checkup at 33 weeks of gestation in October 2009, and consulted at the Breast Disease Center of Shanghai Ruijin Hospital, where hollow-core needle aspiration of the mass was performed. The disease is stable without local recurrence and distant metastasis. We analyzed the diagnosis of benign tumor made by the initial physician based on the patient’s age, clear boundary of the mass and good mobility, which led to the delay of the best time for surgery due to paralysis and hasty conclusion. This led to the delay of surgical treatment, which resulted in the patient’s advanced tumor development at the time of re-visit. Because the malignancy of PABC is often higher than that of non-pregnant and lactating patients, and the disease progresses rapidly, clinicians should be highly alert to patients with palpable breast lumps during pregnancy, and should combine breast ultrasound examination with routine breast physical examination. In case 2, due to the lack of necessary physical examination skills, the doctor mistook the palpable lump as a normal breast hypertrophy and thickening during pregnancy, and did not give necessary further adjuvant examinations, so that the cancer could progress rapidly to locally advanced stage, which not only caused the patient to miss the best treatment period, but also had to endure the physical and mental blow brought by induced abortion, which is really sad! Imagine if the doctor had allowed the patient to undergo a simple breast ultrasound examination when the physical examination was unclear, it might have saved a life and the happiness of a family. These two patients also shared the common feature of blindly trusting the judgment of the primary care physician when the lump continued to increase in size, delaying the best diagnosis and treatment by failing to follow up on time. In case 3, a smaller breast lump was found by the obstetrician during the pregnancy checkup and a definitive diagnosis was recommended, so that the patient received timely and regular treatment, and the birth of a healthy baby will certainly give the mother the courage and confidence to fight the disease. Since the attention of both doctors and patients is often focused on the patient’s abdomen and uterus during routine check-ups of pregnant women, and not enough attention is paid to breast cancer in pregnancy, it is recommended that obstetricians should be vigilant in this regard so as to increase the early detection rate of breast cancer in pregnancy. Breast cancer is a tumor that responds to hormones. The level of estrogen and progesterone in the blood circulation increases during pregnancy, thus accelerating the growth of tumors and promoting their metastasis. In addition, during pregnancy and lactation, the breast gland is obviously enlarged, the breast capillaries increase, the breast is obviously enlarged and hard, the density increases, and the cancer is often hidden by the thickened gland. The treatment of PABC is based on the same principles as that of non-pregnant breast cancer, with the aim of providing the best treatment option for the mother to improve survival while minimizing the impact on the fetus. While total mastectomy is the standard surgical procedure for PABC, a study at the European Society of Oncology meeting in 2005 showed that breast-conserving surgery may be considered for early stage PABC less than 2.4 cm in diameter. Whether adjuvant chemotherapy after surgery has any adverse effect on the fetus has been a common topic of concern for doctors and patients. Although the study reported by Litton, M.D. Anderson Cancer Center in the United States at the ASCO Breast Cancer Forum in 2010 showed that patients with PABC receiving chemotherapy had no significant effect on the fetus and recommended no need to postpone it, domestic experts have cautious reservations about this view and generally agree that Chemotherapy is prohibited in the early 3 months of pregnancy because this is an important stage of fetal organogenesis and is highly susceptible to the teratogenic effects of chemotherapy drugs, while chemotherapy during the 4-9 months of pregnancy is relatively safe. The success of breast cancer treatment depends largely on the stage of the disease at the time of diagnosis, and the detection of an earlier stage of breast cancer is far more significant to the patient than any current treatment options, and is even more critical for PABC patients. Therefore, clinicians are urged to be highly vigilant, to perform meticulous and standardized physical examination, necessary ultrasound examination of the breast, targeted puncture and biopsy pathology, and to strengthen health education for pregnant women about PABC, so that doctors and patients can work together to improve the early diagnosis rate of PABC.