MRI fused with prone FDG PET/CT improves the primary tumour staging of patients with breast cancer.

OBJECTIVE: Our aim was to evaluate the diagnostic accuracy of magnetic resonance imaging (MRI) fused with prone 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in primary tumour staging of patients with breast cancer. METHODS: This retrospective study evaluated 45 women with 49 pathologically proven breast carcinomas. MRI and prone PET-CT scans with time-of-flight and point-spread-function reconstruction were performed with the same dedicated breast coil. The studies were assessed by a radiologist and a nuclear medicine physician, and evaluation of fused images was made by consensus. The final diagnosis was based on pathology (90 lesions) or follow-up ≥ 24 months (17 lesions). RESULTS: The study assessed 72 malignant and 35 benign lesions with a median size of 1.8 cm (range 0.3-8.4 cm): 31 focal, nine multifocal and nine multicentric cases. In lesion-by-lesion analysis, sensitivity, specificity, positive and negative predictive values were 97%, 80%, 91% and 93% for MRI, 96%, 71%, 87%, and 89% for prone PET, and 97%. 94%, 97% and 94% for MRI fused with PET. Areas under the curve (AUC) were 0.953, 0.850, and 0.983, respectively (p < 0.01). CONCLUSIONS: MRI fused with FDG-PET is more accurate than FDG-PET in primary tumour staging of breast cancer patients and increases the specificity of MRI. KEY POINTS: • FDG PET-CT may improve the specificity of MRI in breast cancer staging. • MRI fused with prone 2-[fluorine-18]-fluoro-2-deoxy-D-glucose PET-CT has better overall diagnostic performance than MRI. • The clinical role of fused PET-MRI has not yet been established.