Breast cancer is a common malignant tumor in women, accounting for the second highest number of malignant tumors in women. It also occurs occasionally in men. FDG-PET is valuable in diagnosing the nature of the primary site of breast cancer, lymph node staging, and in patient follow-up after surgery, chemotherapy, and/or external radiation therapy. The main advantage of FDG-PET/CT imaging over conventional imaging is its ability to show the patient’s primary lesion, local recurrence, lymph node metastasis and distant metastasis in a single examination. Early diagnosis and early treatment are the key to cure of breast cancer, and the prognosis of breast cancer is largely determined by several aspects such as morphological manifestation of the tumor, axillary lymph node metastasis (size, location, number) and biological characteristics of the tumor, among which the most influential is the number of lymph node metastasis. The only reliable clinical method is to confirm the tumor metastasis to lymph nodes by surgical excision of local lymph node biopsy pathology. However, in addition to the invasiveness of biopsy, there are still major limitations in terms of enlargement of insignificant lymph nodes or local soft tissue invasion. According to the United States in the 1990s statistics found that up to 400,000 cases of breast error surgery each year. 1. Diagnosis of primary foci Different researchers have come to different conclusions. FDG-PET/C imaging diagnoses primary foci of breast cancer: sensitivity 80-100%, specificity 68-100%. It is important to determine the extent of local infiltration of primary tumors in special areas of the breast, such as tumors close to the chest wall. 2. Monitoring the effect of treatment About 20%-30% of breast cancer patients are not sensitive to chemotherapy. Almost all patients with effective chemotherapy show significantly reduced FDG uptake in local lesions at the early stage of treatment initiation; while patients with ineffective chemotherapy show unchanged local FDG uptake; if the FDG concentration increases in the lesion, it suggests progression of the disease. 3.Metastasis and clinical staging Whether the axillary lymph nodes are infiltrated or not is an important factor affecting the staging of breast cancer and judging the prognosis. It has been reported that the sensitivity of FDG-PET imaging for axillary lymph node detection is 94.4%, specificity is 86.3%, and accuracy is 89.8%. It has been suggested that if the axillary lymph node PET imaging is negative, routine axillary lymph node dissection is not necessary to reduce the corresponding side effects. The diagnosis of lung, brain, liver and other organ metastases is significantly higher than CT and MR, and the diagnosis of osteolytic bone metastases is better than whole-body bone imaging. PET is better than traditional imaging methods (CT, MRI and ultrasound) in diagnosing breast cancer recurrence, especially for patients with high clinical suspicion of recurrence or metastasis after breast cancer treatment (such as elevated serum tumor markers) and negative imaging, and can change the treatment plan of 44% of patients.