Assessing
therapy response of
breast cancer bone
metastases is challenging. In retrospective studies, serial
18F-FDG PET was predictive of time to skeletal-related events (tSRE) and time to progression (
TTP). 18F-NaF PET improves bone
metastasis detection compared with bone scanning. We prospectively tested
18F-FDG PET and 18F-NaF PET to predict tSRE,
TTP, and overall survival (OS) in patients with bone-dominant metastatic
breast cancer (MBC). Methods: Patients with bone-dominant MBC were imaged with
18F-FDG PET and 18F-NaF PET before starting new
therapy (scan1) and again at a range of times centered around approximately 4 mo later (
scan2). Maximum standardized uptake value (SUVmax) and lean body mass adjusted standardized uptake (SULpeak) were recorded for a single index lesion and up to 5 most dominant lesions for each scan. tSRE,
TTP, and OS were assessed exclusive of the PET images. Univariate Cox regression was performed to test the association between clinical endpoints and
18F-FDG PET and 18F-NaF PET measures. mPERCIST (Modified PET Response Criteria in Solid
Tumors) were also applied. Survival curves for mPERCIST compared response categories of complete response+partial response+stable disease versus progressive disease for tSRE,
TTP, and OS. Results: Twenty-eight patients were evaluated. Higher
18F-FDG SULpeak at
scan2 predicted shorter time to tSRE (P = <0.001) and
TTP (P = 0.044). Higher
18F-FDG SUVmax at
scan2 predicted a shorter time to tSRE (P = <0.001). A multivariable model using
18F-FDG SUVmax of the index lesion at scan1 plus the difference in SUVmax of up to 5 lesions between scans was predictive for tSRE and
TTP. Among 24 patients evaluable by
18F-FDG PET mPERCIST, tSRE and
TTP were longer in responders (complete response, partial response, or stable disease) than in nonresponders (progressive disease) (P = 0.007, 0.028, respectively), with a trend toward improved survival (P = 0.1). An increase in the uptake between scans of up to 5 lesions by 18F-NaF PET was associated with longer OS (P = 0.027). Conclusion: Changes in
18F-FDG PET parameters during
therapy are predictive of tSRE and
TTP, but not OS. mPERCIST evaluation in bone lesions may be useful in assessing response to
therapy and is worthy of evaluation in multicenter, prospective trials. Serial 18F-NaF PET was associated with OS but was not useful for predicting
TTP or tSRE in bone-dominant MBC.