Is F-18 FDG PET/CT useful even in low FDG-avidity breast cancer subtypes, compared to breast US or MRI?

Objectives The aim of this study was to evaluate diagnostic performance of F-18 FDG PET/CT in initial axillary lymph node staging and tumor recurrence and/or metastasis in breast cancer subtypes with low FDG-avidity (invasive lobular, mucinous, and tubular carcinomas) in comparison to breast ultrasonogram (US) and/or magnetic resonance imaging (MRI).

Methods This was a retrospective study in which a total of 491 FDG PET/CT exams from 192 patients with biopsy proven breast cancer subtypes with low FDG-avidity were identified between January 2009 and March 2015. Nodal status on initial staging and local tumor recurrence or metastasis on surveillance was confirmed either by pathology or further follow-up studies. Comparison was made with recent US and/or MRI taken within 2 weeks. The sensitivity and specificity of FDG PET/CT, US, and MRI were evaluated and compared using the McNemar’s test.

Results Of the total 491 FDG PET/CT scans, 142 were for initial staging, and 349 for surveillance. For the initial staging, 144 lesions from 142 patients were included. Among these, 127 lesions had perceptible FDG uptake (mean SUVmax 2.7 ± 1.9). For detection of axillary lymph node metastasis at initial staging, the sensitivity and specificity were calculated as 51.5% and 94.6% for FDG PET/CT, 42.4% and 90.1% for US and 51.5% and 88.3% for MRI, respectively. PET/CT showed significantly higher specificity than MRI (p=0.039). In the surveillance group, PET/CT showed comparable diagnostic performance for local tumor recurrence compared to US (p=0.07). There were 8 sites of distant metastasis in 5 patients, and all of these were identified only by PET/CT (4 of bones, 1 of ovary, 1 of uterus, and 2 of liver).

Conclusions Performance of FDG PET/CT in invasive lobular, mucinous, and tubular carcinomas of breast cancer showed higher specificity compared to MRI and comparable sensitivity and specificity compared to US in terms of detecting initial metastatic axillary lymph nodes. FDG PET/CT also showed comparable performance to US in terms of local tumor recurrence. FDG PET/CT detected unexpected distant metastasis in 5 patients. Therefore F-18 FDG PET/CT is useful for axillary lymph node staging and detecting tumor recurrence even when the primary breast cancer has low FDG-avidity.