Utility of High-Resolution Semiconductor Positron Emission Tomography/Computed Tomography in the Assessment of Breast Cancer Extent: Comparison with Magnetic Resonance Imaging.

OBJECTIVE: This study aims to compare the potential of whole-body silicon photomultiplier positron emission tomography/computed tomography (WB SiPM PET/CT) in the prone position with dynamic magnetic resonance imaging (MRI) in determining the extent of breast cancer. METHODS: This retrospective study included 77 patients with 84 breast cancers who underwent both PET/CT and MRI, excluding those who received neoadjuvant chemotherapy. Four tumour thresholds for 18F-fluorodeoxyglucose uptake were defined based on the mean standardised uptake value (SUVmean) and standard deviation (SD) of normal breast tissue: SUVmean+2SD, SUVmean+3SD, 1.5SUVmean+2SD, and 1.5SUVmean+3SD. Semiautomatic measurements of tumour size for each threshold and MRI were compared against pathological tumour size and analysed by menopausal status and Ki-67 expression. RESULTS: PET/CT failed to visualise two lesions. No significant differences in the image-to-pathological tumour size ratio were observed between MRI and the 1.5SUVmean+2SD. All MRI and SUV threshold measurements exhibited strong correlations with pathological size. The 1.5SUVmean+2SD demonstrated the highest pathological concordance rate, comparable to MRI. Subgroup analysis revealed that the 1.5SUVmean+2SD was superior for premenopausal patients (60.6%, p < 0.05), while MRI excelled in postmenopausal patients (61.2%). Both 1.5SUVmean+2SD and MRI achieved the highest concordance rates (62.2%) in the high-Ki-67 group. CONCLUSION: The 1.5SUVmean+2SD of prone WB SiPM PET/CT offers a diagnostic performance equivalent to MRI for assessing breast cancer extent, particularly in premenopausal patients, while MRI remains optimal for postmenopausal patients. Both modalities are also highly effective in high Ki-67 tumours. ADVANCES IN KNOWLEDGE: These findings highlight the potential of high-resolution semiconductor PET/CT for assessing breast cancer extent.