Interim PET scan during prostate cancer therapy tailors treatment

Adding a scan during a patient’s prostate cancer therapy can help personalize treatment, according to research presented at the Society of Nuclear Medicine and Molecular Imaging (SNMMI)’s 2019 Annual Meeting in Anaheim, Calif.

Results of study found prostate-specific membrane antigen (PSMA) PET imaging in patients with metastatic castration-resistant prostate cancer after two cycles of lutetium-177 (177Lu)-PSMA radioligand therapy helped predict patient survival.

“Tumor response was assessed by the changes in PSMA-avid tumor volume from baseline to the second PSMA PET using three classification methods,” Andrei Gafita, MD, with Klinikum rechts der Isar hospital, Technical University Munich in Germany, said in an SNMMI release. “Subsequently, we found that tumor response assessed on interim PSMA PET after two RLT cycles was associated with overall survival.”

Statistics from the National Cancer Institute put the five-year survival rate for men with metastatic cancer at 30.5%. Phase II trials in such patients treated with 177Lu-PSMA therapy have produced promising results, the authors noted. And while such therapy uses a preliminary PSMA PET scan to choose patients eligible for radioligand therapy, use of an interim PET scan has only been explored for lymphoma patients, with positive results.

Therefore, Gafita and colleagues retrospectively analyzed patients who underwent gallium-68 (68Ga)-PSMA11 PET/CT at baseline and after two cycles of 177Lu-PSMA RLT under a compassionate use program.

Instead of using traditional standardized uptake value, the team used pPSMA, an in-house software program, to evaluate the whole-body tumor burden.

“Our results…show that interim PSMA PET can be used for therapeutic response assessment in patients undergoing 177Lu-PSMA RLT,” Gafita explained. “Furthermore, occurrence of new lesions in PSMA PET is a prognostic factor for disease progression and could be included in defining tumor response based on PSMA PET imaging.”

“While further analyses involving clinical parameters are warranted,” Gafita added, “this analysis paves the way for use of interim PSMA PET in a prospective setting during 177Lu-PSMA radioligand therapy."