$^{18}F-FDG$ PET in combination with conventional imaging modalities could help avoid unnecessary biopsy for the primary mass, and it also has a high diagnostic accuracy in patients with dense breasts. In the assessment of metastasis, $^{18}F-FDG$ PET was useful to select patients who required sentinel lymph node biopsy and to detect extra-axillary lymph node metastasis and distant metastasis. To increase the sensitivity for osteoblastic bone metastasis, bone scintigraphy should be added. In the detection of recurrence, $^{18}F-FDG$ PET showed a higher diagnostic accuracy than tumor marker or computed tomography, and therefore it can be used in routine breast cancer follow-up. $^{18}F-FDG$ PET has been reported that it correctly predicted the response of neoadjuvant chemotherapy on as early as 8th day of treatment. Therefore, it is useful for the early detect of therapeutic response in advanced breast cancer.