Abstract
180 Background: CRPC is frequently associated with the development of osseous metastases. While imaging allows treatment response determination in soft tissue metastasis, its application in bony metastasis is limited to staging. Methods: QTBI is an innovative tool that allows extraction of comprehensive functional information in all osseous metastases, as well as treatment response in individual lesions, using 18F-Sodium Fluoride (NaF) PET/CT. We completed a multi-center trial assessing the performance characteristics (test-retest) and responsiveness of QTBI as an imaging biomarker of treatment response in men with metastatic CRPC to bone treated with either a taxane-based or androgen-signaling pathway directed therapy. Results: 54 patients have been enrolled from three academic centers. Potential imaging biomarkers of treatment response have been identified. Here we present initial data regarding the inter-lesional response heterogeneity and implications. Conclusions: Changes in SUVmax, SUVtotal, and SUVmean reflect quantifiable PET measurements that are complementary, but may have different meaning depending on the treatment administered (cytotoxic vs cytostatic). Relying on one measure alone can be misleading, particularly when assessing treatment response. For example, some lesions may experience a decrease in SUVmax, while simultaneously having an increase in SUVtotal. This implies that the therapy decreased the max functional activity of the lesion, but the overall functional burden of the lesion increased analogous to “slowing down” progression. This is in contrast with lesions that decrease (increase) in both SUVmax and SUVtotal, which would imply decreased activity and burden (increased activity and burden). We will show data representative of the above along with clinical outcomes in support of this conclusion, as well as the implications of treatment response heterogeneity in the clinical outcome. In summary, QTBI provides a unique tool in understanding the dynamics of treatment response, allowing newer trial designs that can explore combination, sequence, and the issue of continuing treatment beyond progression with existing therapies. Clinical trial information: NCT01516866.
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