Assessment of Bone Lesions with 18F-FDG-PET Compared to 99mTechnetium Bone Scintigraphy Leads to Clinically Relevant Differences in Metastatic Breast Cancer Management.

Rationale: Whether assessment of potential bone lesions in metastatic breast cancer (MBC) by means of 18F-fluorodeoxyglucose (FDG)-PET instead of 99mTechnetium (99mTc) bone scintigraphy (BS) supports clinically relevant changes in MBC management, is currently unknown. Therefore, we retrospectively compared the management recommendations based on bone lesion assessment by FDG-PET plus contrast enhanced computed tomography (ceCT) or BS plus ceCT, for patients with newly diagnosed MBC. Methods: Baseline ceCT, BS and FDG-PET of all patients included in the IMPACT-MBC study (NCT01957332) at location University Medical Center Groningen (UMCG), were reviewed for bone lesions. In case of bone lesions on any imaging modality, virtual MBC management recommendations per patient were made by a multidisciplinary expert panel, based on either FDG-PET plus ceCT, or BS plus ceCT. The panel had access to standard clinicopathological information and baseline imaging findings outside the skeleton. Clinically relevant management differences between the two recommendations were defined as 1) different treatment intent, (curative, non-curative or unable to determine and/or 2) different systemic or local treatment. In case of absence of bone lesions with any imaging modality, patients were included in the analyses without expert review. Results: A total of 3,473 unequivocal bone lesions was identified in 102 evaluated patients (39% by ceCT, 26% by BS, 87% by FDG-PET). Additional bone lesions on FDG-PET plus ceCT compared to BS plus ceCT led to change of MBC management recommendations in 16% of all patients (95% confidence interval (CI) 10-24%). BS also changed management compared to FDG-PET in one patient (1%; 95%CI 0-5%). In 26% (95%CI 19-36%) of patients, an additional FDG-PET was requested, because BS provided insufficient information. Conclusion: In this exploratory analysis of newly diagnosed MBC patients, FDG-PET versus BS to assess bone lesions, resulted in clinically relevant management differences in 16% of all patients. BS delivered insufficient information in over one fourth of patients, resulting in additional request for FDG-PET. Based on this data, FDG-PET should be considered as primary imaging modality for assessment of bone lesions in newly diagnosed MBC.