Diagnostic Performance of [18F]FES PET/CT for Axillary LN Metastasis in Invasive Lobular Carcinoma

Inclusion Criteria: * Male or female subjects aged 19 years or older regardless of race/ethnicity. * Subjects with histologically confirmed estrogen receptor-positive invasive lobular breast cancer within 90 days prior to \[18F\]FES PET/CT imaging * Subjects whose primary tumor of cT1-3 according to the American Joint Committee on Cancer (AJCC) 8th tumor staging system * Subjects with suspected or confirmed axillary lymph node metastasis clinically or in imaging test (ultrasound) * Subjects who scheduled to undergo sentinel node biopsy or axillay lymph node dissection within 90 days of \[18F\]FES PET/CT imaging * Subjects whose Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 2 points or less Exclusion Criteria: * Subject or the subject's legally acceptable representative does not provide written informed consent form * Subjects with confirmed or suspected large, bulky, matted cN2 or cN3 axillary lymph node metastases, or distant metastases. * Previous history of ipsilateral axillary lymph node dissection, sentinel lymph node surgery, or lymph node dissection biopsy. * Patients who are scheduled for or have undergone chemotherapy, radiotherapy, antihormone therapy, targeted therapy, or immunotherapy between \[18F\]FES PET/CT and pathological diagnosis * Subjects who are pregnant or lactating. Exclusion of the possibility of pregnancy is made by one of the following: 1) Physiologically menopausal (menstruation has stopped for more than 2 years), 2) Surgi…