WE-FG-202-05: Quantification of Bone Flare On [F-18] NaF PET/CT in Metastatic Prostate Cancer

Authors


Abstract

Purpose:

Bone flare has been observed on Tc-99m bone scans during early assessment in metastatic Castration-Resistant Prostate Cancer (mCRPC) patients receiving select androgen-signaling pathway (AR) targeted treatments, including CYP17-inhibitor Abiraterone. This study investigates the appearance and potential clinical impact of bone flare in mCRPC patients receiving CYP17-inhibitors using 18F-NaF PET/CT.

Methods:

Twenty-three mCRPC patients being treated with CYP17-inhibitors received NaF PET/CT scans at baseline, week 6, and week 12 of treatment. Individual lesions were identified using a SUV>15 threshold within skeletal regions and articulated bone registration was used to track lesions between scans. Standard SUV metrics were extracted globally for each patient (pSUV) and for each individual lesion (iSUV). Differences in metrics across time-points were compared using Wilcoxon signed-rank tests. Cox proportional hazard regression analyses were conducted between global metrics and progression-free survival (PFS).

Results:

Nineteen patients (83%) showed increasing NaF PET global metrics at week 6, with pSUVtotal reflecting consensus change across other global metrics with median increase +33% (range +2 to 205%). Of these patients, 14 showed subsequent decrease in pSUVtotal, with a median of −17% (range −76 to −1%), indicating flare phenomenon. Increasing pSUVmean at week 6 correlated with extended clinical PFS (HR = 0.58, p=0.02). New lesions did not account for the initial increase in global NaF metrics. Lesion-level analysis reveals 316 lesions in the 14 patients exhibiting global flare. On average, 75% (sd: 22%) of lesions follow global trends with iSUVtotal increasing at week 6 and 65% (sd: 17%) showing iSUVtotal decrease at week 12.

Conclusion:

Bone flare was detected on NaF PET/CT in the first 6 weeks of treatment for mCRPC patients receiving CYP17-inhibitors, subsiding by week 12. Characterization provided in this study suggests prolonged PFS in patients showing bone flare early in select AR-directed treatments.

Prostate Cancer Foundation

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