Clinical relevance of 18F-FDG-negative osteoblastic metastatic bone lesions noted on PET/CT in breast cancer patients.

Purpose: Our study aims to assess the clinical relevance of fluorine-18 fluorodeoxyglucose (F-FDG) negative osteoblastic metastatic bone lesions noted on PET/computed tomography (CT) in breast cancer patients.

Patients And Methods: The medical records of breast cancer patients were reviewed retrospectively from January 2012 until April 2015. We included the patients who had metastatic bone disease evaluated by F-FDG-PET/CT. Group 1 included patients with newly diagnosed metastatic bone disease at the time of imaging and group 2 included patients with a history of treated metastatic bone disease at the time of imaging. Functional and structural bone abnormality was monitored on F-FDG-PET/CT scans.

Results: Fifty-three patients, median age 47.1 years (range 27-80 years), were included. Group 1 included 35 patients. Of those, 88% had predominantly F-FDG-avid osteolytic and mixed lesions (destructive pattern). Complete response was noted in 65% of the patients after treatment, evidenced by disappearance of bony focal activity with partial or total ossification of most osteolytic lesions converting into mixed and 'secondary' osteoblastic lesions. In addition, more ossified lesions were noted in some patients whose lesions were left untreated for long time (aged lesions). The remaining 12% of group 1 patients had pure 'primary' osteoblastic lesions (nondestructive pattern), which started small and expanded with time and tend to be F-FDG-negative. Group 2 included 18 patients who had predominantly mixed and 'secondary' osteoblastic lesions.

Conclusion: We described two types of osteoblastic metastatic bone lesions in breast cancer patients: 'primary' and 'secondary'. 'Secondary' lesions (88%) are totally ossified (healed) osteolytic lesions and are almost always F-FDG-negative on PET/CT. These lesions are of no clinical importance. Healing is potentially seen after treatment or if the lesions are left untreated for a long time (aged lesions). 'Primary' lesions (12%) are seen without previous bone destruction and tend to be F-FDG-negative, although they contain tumor cells. Hence, sequential CT is more helpful than sequential FDG-PET in following 'primary' lesions.