Simultaneous whole-body ¹⁸F-FDG PET-MRI in primary staging of breast cancer: a pilot study.

PURPOSE: Accurate initial staging in breast carcinoma is important for treatment planning and for establishing the likely prognosis. The purpose of this study was to assess the utility of whole body simultaneous (18)F-FDG PET-MRI in initial staging of breast carcinoma.

METHODS: 36 patients with histologically confirmed invasive ductal carcinoma underwent simultaneous whole body (18)F-FDG PET-MRI on integrated 3T PET-MR scanner (Siemens Biograph mMR) for primary staging. Primary lesion, nodes and metastases were evaluated on PET, MRI and PET-MRI for lesion count and diagnostic confidence (DC). Kappa co relation analysis was done to assess agreement between the satellite, nodal and metastatic lesions detected by PET and MRI. Histopathology, clinical/imaging follow-up served as the reference standard.

RESULTS: 36 patients with 37 histopathologically proven index breast cancer were retrospectively studied. Of 36 patients, 25 patients underwent surgery and 11 patients received systemic therapy. All index cancers were seen on PET and MR. Fused PET-MRI showed highest diagnostic confidence score of 5 as compared to PET (median 4; range 3-5) and MRI (median 4; range 4-5) alone. 2/36 (5.5%) patients were detected to have unsuspected contralateral synchronous cancer. 47 satellite lesions were detected on DCE MRI of which 23 were FDG avid with multifocality and multicentricity in 21 (58%) patients. Kappa co relation analysis revealed fair agreement for satellite lesion detection by the two modalities (κ=0.303; P=0.003). The study showed a sensitivity of 60% and 93.3% on PET and MRI respectively for detection of axillary lymph nodes with a specificity of 91% for both and a false negative rate of 6.7% on MRI and 40% on PET. Kappa co relation analysis between PET and MRI for all the lymph nodes detected revealed fair agreement by the two modalities (κ=0.337; P=0.000). Combined PET-MRI increased diagnostic confidence for nodal involvement (median DC 5, range 4-5; P<0.05). Distant metastases were found in 8/36 (22%) patients at the time of diagnosis with a total of 91 metastatic lesions on PET (DC≥4) and 105 on MRI (DC≥4), the difference being statistically significant (P=0.001) while Kappa co relation analysis showed significant agreement between the two modalities (κ=0.667; P=0.000). Overall PET-MRI led to a change in management in 12 (33.3%) patients.

CONCLUSION: In this pilot study, simultaneous (18)F-FDG PET-MR, has been found to be useful in whole-body initial staging of breast cancer patients.