Abstract 605P
Background
Current and emerging PET platforms will enhance the ability to evaluate metastatic lesions in mCRPC. It remains unclear how the evolution of new lesions on more sensitive scans can improve clinical care as all current therapeutics were developed using CT Scan and Tc99m-MDP (Tc99) bone scans. 18F-Sodium Fluoride (NaF) PET imaging has increased sensitivity for bone lesions relative to Tc99. Here we test a semi-automated method of assessing NaF PET using a novel technology.
Methods
18 patients (pts) with mCRPC were treated with enzalutamide +/- prostvac on a trial (NCT01867333) with no improvement in combination allowing for collective analysis. Pts had serial CT, Tc99, and NaF PET scans and were treated until radiographic progression (rPD) regardless of PSA. Lesions on NaF were automatically detected and matched across timepoints using AIQ technology as previously published (Kyriakopoulos, JCO, 2020). Lesion response was categorized as completely responding, partially responding, stable, progressive disease, or new lesions (either completely new or return of a resolved lesion).
Results
18 mCRPC pts were evaluated with serial NaF scans (median PSA: 8.2 ng/ml, age: 65 years, time on treatment: 21 months). 14 pts ultimately had rPD on conventional imaging. In total, 67 serial NaF were evaluated. 233 lesions completely resolved after starting treatment; 52 (22%)of which eventually returned while on therapy. 394 new lesions were seen but 112 (28%) resolved. 14/18 pts (78%) had new lesions that ultimately improved after appearing. In 14 pts who eventually had disease progression, there was an average of 11.7 new lesions vs. baseline on the NaF closest to rPD. In 4 pts who had stable Tc99 throughout there were an average of 9.8 new lesions seen on serial NaF.
Conclusions
These data highlight the dynamic changes seen on PET imaging in mCRPC treated with enzalutamide. The development of new lesions seen on NaF scan may actually resolve in the future and may not predict rPD seen on Tc99. These data highlight that as new PET imaging emerges in mCRPC, more understanding is required as to the clinical significance of new lesions seen on PET imaging in pts with stable disease on Tc99 scans.
Clinical trial identification
NCT01867333.
Editorial acknowledgement
Legal entity responsible for the study
National Cancer Institute, Bethesda, MD, USA.
Funding
Astellas/Pfizer, Bavarian Nordic.
Disclosure
A.J. Weisman, T.G. Perk, S.D. Yip: Financial Interests, Personal, Full or part-time Employment: AIQ. All other authors have declared no conflicts of interest.