To plan optimal management in a patient with breast cancer (BC), accurate baseline staging and early detection and staging of recurrence are necessary.1-3 Representatives from the European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI) recently published the joint European-American guidelines on the role of 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography ([18F]FDG-PET/CT) in no special type (NST) BC, endorsed by several other imaging and clinical societies: the American College of Radiology (ACR), European Society of Surgical Oncology, European Society for Radiotherapy and Oncology (ESTRO), European Society of Breast Imaging, European Society of Radiology, and European Society of Breast Cancer Specialists (EUSOMA).1 Considering the low [18F]FDG-avidity in invasive lobular carcinoma (ILC), the EANM-SNMMI guidelines focused on NST BC. Guidelines from clinical societies such as the American National Comprehensive Cancer Network (NCCN),4 European Society for Medical Oncology (ESMO),5-7 and Advanced Breast Cancer (ABC) international consensus guidelines8 also evaluate imaging techniques, but they include all histological subtypes of BC. There is a lack of consistency in the optimal utilization of [18F]FDG-PET/CT among published guidelines. This manuscript summarizes available evidence, emphasizes the value of [18F]FDG-PET/CT for staging and restaging of patients with BC, and highlights agreements and discrepancies among international guidelines.

Purpose
The recently released EANM/SNMMI guideline, endorsed by several important clinical and imaging societies in the field of breast cancer (BC) care (ACR, ESSO, ESTRO, EUSOBI/ESR, EUSOMA), emphasized the role of [18F]FDG PET/CT in management of patients with no special type (NST) BC. This review identifies and summarizes similarities, discrepancies and novelties of the EANM/SNMMI guideline compared to NCCN, ESMO and ABC recommendations.

Methods
The EANM/SNMMI guideline was based on a systematic literature search and the AGREE tool. The level of evidence was determined according to NICE criteria, and 85 % agreement or higher was reached regarding each statement. Comparisons with NCCN, ESMO and ABC guidelines were examined for specific clinical scenarios in patients with early stage through advanced and metastatic BC.

Results
Regarding initial staging of patients with NST BC, [18F]FDG PET/CT is the preferred modality in the EANM-SNMMI guideline, showing superiority as a single modality to a combination of contrast-enhanced CT of thorax-abdomen-pelvis plus bone scan in head-to-head comparisons and a randomized study. Its use is recommended in patients with clinical stage IIB or higher and may be useful in certain stage IIA cases of NST BC. In NCCN, ESMO, and ABC guidelines, [18F]FDG PET/CT is instead recommended as complementary to conventional imaging to solve inconclusive findings, although ESMO and ABC also suggest [18F]FDG PET/CT can replace conventional imaging for staging patients with high-risk and metastatic NST BC. During follow up, NCCN and ESMO only recommend diagnostic imaging if there is suspicion of recurrence. Similarly, EANM-SNMMI states that [18F]FDG PET/CT is useful to detect the site and extent of recurrence only when there is clinical or laboratory suspicion of recurrence, or when conventional imaging methods are equivocal. The EANM-SNMMI guideline is the first to emphasize a role of [18F]FDG PET/CT for assessing early metabolic response to primary systemic therapy, particularly for HER2+ BC and TNBC. In the metastatic setting, EANM-SNMMI state that [18F]FDG PET/CT may help evaluate bone metastases and determine early response to treatment, in agreement with guidelines from ESMO.

Conclusions
The recently released EANM/SNMMI guideline reinforces the role of [18F]FDG PET/CT in the management of patients with NST BC supported by extensive evidence of its utility in several clinical scenarios.