The aim of this prospective study was to evaluate the correlation of primary tumor metabolic activity parameters; maximum standardized uptake value (SUVmax) and tumor SUVmax/liver average SUV ratio (TLR) with clinical, histopathological and molecular characteristics of initial staging breast cancer (BC) patients using 18F-fluorodeoxyglucose (FDG) positron emission tomography / computerized tomography (PET/CT) scan. Forty female patients with newly diagnosed BC were enrolled in our study, age ranging from 31-78 years (mean 50.5 +/- SD11.7). All the primary tumors were detected with mean SUVmax 10.8(+/-SD 7.9). The mean /median SUVmax values of primary tumor was higher in premenopausal , stage III and IV, Estrogen Receptors negative( ER-), Progesterone Receptors negative(PR-), Human epidermal growth factor receptor 2 positive ( Her2neu+) patients, high nuclear grade (GIII), triple negative molecular subgroup (TN) and positive axillary lymph node (ALNs) metastasis,(P= 0.003, 0.017, 0.113, 0.089 0.01 ,0.002 , 0.007 and 0.016 respectively). The mean/median TLR values was higher in premenopausal ,Her2neu+, GIII, TN molecular subtype patients, stage III and IV and in patients with positive ALNs , ER- and PR - patients (P= 0.002, 0.0476 , 0.005 , 0.018 , 0.039 and 0.022, 0.095 and 0.129 respectively). SUVmax of the primary lesion and TLR were moderately negatively correlated with the age of the patients (P= 0.005 and 0.008 respectively), also they were moderately positively correlated with the size of the primary tumor (P= 0.019 and 0.036 respectively). TLR was predictive of nodal involvement AUC= 0.612 (95% CI: 0 …