Abstract
1806
Objectives FDG PET/CT is useful to assess changes in bmets in BrCa patients (pts) under treatment (Tx). However validation is problematic due to absence of tissue diagnosis from bmets. We examined combined changes in FDG uptake and CT results over follow up (f/u) scans, aiming to identify prognostic patterns.
Methods We retrospectively analyzed PET/CT scans of 42 BrCa pts with increased FDG uptake (PET+) in bmets, and with 2-9 scans over 6-57 months f/u. All pts received chemo/hormone and bisphosphonate Tx. CT bone lesions corresponding to PET foci were categorized as blastic (bl), lytic (lyt) or negative (CT-). Multiple bone foci with the same PET and CT characteristics in a single scan were grouped together as one finding.
Results Mean time intervals between scans were 6 months. On scan 1, 54 PET+ bone findings were identified. On scan 2, 34/54 were PET+ (15 bl, 12 lyt, 7 CT-) and 20 PET- (15 bl, 0 lyt, 5 CT-) which remained PET- on all available f/u. Of the 34 PET+ findings on scan 2, 10 (4 bl, 5 lyt, 1 CT-) remained PET+ on scan 3, and 5 became PET- on scans 4-9 with CT changing from lytic to blastic in 2; 17 (7 bl, 6 lyt, 4 CT-) became PET- on scan 3, with CT changing from lytic (6) and CT- (3) to blastic. In all, 36/54 findings became PET-/bl and remained PET- on f/u. There were no PET-/lyt findings.
Conclusions Three main patterns of behavior of BrCa bone mets under Tx emerged: lesions becoming PET-/bl are compatible with response to Tx; a flare phenomenon can explain transient ongoing FDG uptake in PET+/bl lesions; lytic lesions remaining PET+ do not respond to Tx. Larger studies with clinical and biologic correlates are required to validate the significance of these combined PET/CT results
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