Objective To investigate the characteristics of 18F-Alfatide II PET/CT imaging in normal breasts and breast cancer lesions.Methods From March 2016 to August 2017,22 female patients(age:(52±10)years)with suspected breast malignant nodules or masses were prospectively enrolled.All patients underwent 18F-Alfatide II PET/CT imaging prior to biopsy or surgery.The imaging characteristics of normal breasts were assessed visually and the difference of maximum standardized uptake value(SUVmax)in normal breasts and uterus between patients with and without menopause was compared,SUVmax of cancer lesions and normal breasts was also compared.Breast cancer lesions were classified according to the distribution characteristics of radioactive uptake,and molecular subtypes ware determined by immunohistochemistry and fluorescence in situ hybridization.The SUVmax of different morphological and molecular subtypes were analyzed.Two-sample t test and Pearson or Spearman correlation analysis were used to analyze the data.Results There were 23 breast cancer lesions(one patient had bilateral breast cancer lesions and one had a history of one-side breast resection),20 normal breasts and 21 normal uteruses.Those normal breasts and uteruses didn't show any malignant change after being followed up for more than 1 year(one patient had uterine fibroids resection).There was a slight increase of radioactivity uptake in the cord-like connective tissue region at the margin of the gland in 11 mammary glands,and the SUVmax was higher than that of glandular tissue in the central region(1_81±0.67 vs 0.79±0.37;t = 6.771,P<0.00l).Of the 11 cases,except for one patient whose uterus was removed,the other 10 patients were accompanied by increased diffuse radioactivity of the uterus.SUVmax of 19 normal breast connective tissues(1.31±0.80)and uterus(3.80+1.79)were positively correlated(r = 0.785,P<0.05).For patients with/without menopause(n= 11 each group),the SUVmax of normal breast connective tissues(0.72±0.39 vs 1.81±0.67)and uterus(2.04±0.39 vs 5.11 + 1.06)were significantly different(t values:4.42 and 8.66,both P<0.01).Different levels of radioactive uptake were observed in all 23 breast cancer lesions,with SUVmax of 6.93±3.97,which was significantly higher than the nipple,connective tissue and glandular tissue of normal breasts(t values:6.784-7.559,all P<0.05).According to the characteristics of the radioactivity uptake distribution of the lesion,among the 23 breast cancer lesions,5 were mass type,3 were nodular type,4 were diffuse type,and 11 were multi-focal/multi-center type,and the SUVmax of multi-focal/multi-center type was the highest(F=3.55,P<0.05).The SUVmax of basal-like breast cancer lesions(2.49±1.67)was lower than the other three molecular subtypes.Lesions with high level human epidermal growth factor receptor 2(HER2)positive expression had higher SUVmax.Conclusions 18F-Alfatide II PET/CT imaging shows that normal breasts have a slight radioactive distribution,mainly concentrate in the nipple and connective tissues around the glandular,and the uptake have a positive correlation with the radioactive uptake of the uterus.The degree of radioactive uptake of breast cancer lesions is significantly higher than that of normal breasts.Breast cancer lesions with different moqjhological features all have obvious radioactive uptake,especially the multi-focal/multi-center type.Different molecular subtypes have different radioactive uptake levels.SUVmax is lower in basal-like breast cancer lesions,and higher in HER2 positive expression lesions.