Comparison between 18F-FDG and 18F-NaF PET imaging for assessing bone metastases in breast cancer patients: a literature review

Abstract

In patient with breast cancer (BC), 18F-FDG PET/CT is widely used for assessing skeletal metastatic involvement. Also 18F-NaF PET imaging is considered an accurate modality for detecting bone metastases. We aimed to review current literature on comparative performances of 18F-FDG and 18F-NaF PET imaging for assessing bone metastases from BC. A literature search for PET studies published in PubMed/MEDLINE database in the last 10 years (September 2009–September 2019) using both 18F-FDG and 18F-NaF to detect bone involvement in BC patients was conducted, based on the combination of the terms (“PET” OR “positron emission tomography”) AND ((“FDG” OR “fluorodeoxyglucose” AND “fluoride” OR “NaF”)) AND “breast cancer”. Data on clinical and methodological aspects and diagnostic performances between the two tracers were collected and compared. Out of 43 studies initially retrieved, 12 studies (overall 340 patients) were finally considered, 3/12 performing a combined 18F-FDG/18F-NaF (“cocktail”) imaging. Heterogeneity in several aspects has been found among studies. However, 18F-NaF PET demonstrated overall higher sensitivity than 18F-FDG (ranging from 91.7 to 100% and from 41.6 to 75%, respectively), potentially impacting on patients’ management, but with lower specificity due to non-tumor-specific bone uptake (ranging from 46.3 to 76.2% and from 94.3 to 99%, respectively). 18F-FDG only is able to detect early metastases confined to bone marrow. Occurrence of “flare phenomenon” limits the use of 18F-NaF for assessing early treatment response. Cocktail imaging may allow the most comprehensive evaluation of bone involvement, moreover with dosimetry advantages over two single-tracer PET scans, but losing prognostic information carried by 18F-FDG. Both 18F-NaF and 18F-FDG are suitable for assessing skeletal involvement in BC patients. However, inherent different uptake mechanism highlights differences in diagnostic performance between these tracers, reflecting specific bone metastases’ characteristics. Therefore, a complementary use of 18F-NaF and 18F-FDG PET imaging may be considered in clinically selected BC patients, such as those with suspicious bone involvement despite negative 18F-FDG PET imaging, with prevalent CT-sclerotic bone findings or with apparently confined or oligo-metastatic cancer to exclude widespread disease.