Review of the role of MRI and 18F-sodium fluoride PET/computed tomography in the characterisation of spinal bone metastases in a cohort of patients with breast cancer.

PURPOSE: The purpose of the study was to compare the diagnostic accuracy and relative usefulness of MRI and 18F-NaF (sodium fluoride) PET/computed tomography (CT) for detection of spinal bone metastases in a cohort of patients with high-risk breast cancer (BrCa).

METHODS: A retrospective study was conducted of patient and lesion-based analyses on 66 consecutive patients (median age, 62.5 years; age range, 33-91 years) who underwent Spinal MRI as well as 18F-NaF PET-CT for restaging of newly diagnosed recurrent BrCa with no previous bone metastases. Both scans were performed within 20 days of each other. Review of prior images, clinical decisions, multi-disciplinary team discussions and decisions as well as follow-up information including scans and definitive tests was performed at least 12 months after the initial scans.

RESULTS: Of the 66 patients reviewed, 26 patients had documented spinal bone metastases on one or both modalities, while 40 patients were considered bone disease free on both modalities and this was confirmed on follow-up. On lesion-based analysis, the findings of 18F-NaF PET-CT and spinal MRI were concordant in 51 patients (77.3%). In the remaining patients, 18F-NaF PET/CT detected more lesions in 4 patients (7.6%) and MRI detected more lesions in 10 patients (15.1%). Interestingly, there was a very high, 97 % concordance (64 patients) between spinal MRI and 18F-NaF PET-CT when staging of spinal bone metastasis was taken into consideration. In one patient MRI identified two spinal bone metastases which were not seen on 18F-NaF PET/CT; and, in one patient 18F-NaF PET/CT showed few spinal bone metastases when no lesion was seen on MRI.

CONCLUSIONS: Our study showed a high level of concordance between 18F NaF PET-CT and spinal MRI within the setting of detection of bone lesions in the spine in a cohort of patients with high-risk BrCa. In our opinion, this high level of concordance negates the need to perform both tests although each test may be indicated for slightly different reasons. Further longitudinal studies across a longer duration and more centres may provide more definitive answers.