(UroToday.com) At the 2022 American Society of Clinical Oncology Annual Meeting held in Chicago and virtually, the poster session focused on Prostate, Testicular, and Penile cancers on Monday afternoon included a presentation from Dr. Philip Sutera discussing the association prostate specific membrane antigen (PSMA) response and radiographic-progression free survival among patients treated with stereotactic ablative radiation therapy in oligometastatic castration-sensitive prostate cancer (omCSPC).
The increasing utilization of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) for patients with the biochemically recurrent disease following local therapy has allowed the detection of small and/or atypically localized metastatic prostate cancer lesions. The question of the best management of these patients is somewhat unclear. There is increasing interest in metastasis-directed therapy (MDT) which emerging data has shown to improve outcomes Prostate-specific membrane antigen positron emission tomography (PSMA-PET/CT) can detect occult metastatic disease and has been proposed as a biomarker for treatment response. In this study, the authors sought to identify and validate a PSMA-PET biomarker for clinical outcomes following MDT in omCSPC.
To do so, the authors performed an international multi-institutional retrospective study of two independent cohorts of men with omCSPC who were treated with metastasis-directed stereotactic ablative radiation therapy (SABR) and underwent PSMA-PET/CT prior to and 3-6 months after treatment. In this context, omCSPC was defined as 3 or fewer lesions.
Pre- and post-SABR PSMA-PET/CT standardized uptake value (SUV) was measured for all lesions and PSMA response defined discretely using a cutpoint of ≥ 30% decrease in SUVmax. PSMA-PET response was correlated with lesion local control (LLC), radiographic progression-free survival (rPFS) defined using conventional and PET imaging, and metastasis-free survival (MFS) defined by conventional imaging alone.
The authors included 131 patients with 261 treated metastases in the analysis. Patients were followed for a median of 29 months (IQR 18.5-41.3). Following SABR, 78.4% of lesions experienced a partial or complete PSMA response.
In multivariable models, SUV response was significantly associated with improved lesion local control (HR = 9.97, 95%CI 3.92-25.4; p < 0.01). Patients with PSMA response in all lesions experienced significantly better rPFS (HR = 0.49, 95%CI 0.26-0.92; p = 0.03) compared to their counterparts and this maintained significance within both the discovery (p < 0.01) and validation (p = 0.01) cohorts. Within the discovery cohort, patients with PSMA response in all lesions also experienced significantly improved MFS (HR = 0.24, 95%CI 0.07-0.85; p = 0.03).
Building on this work, the authors are seeking to analyse this model in an independent validation cohort. However, based on these data, PSMA-PET response is a robust and externally validated radiographic biomarker for rPFS following SBRT, and appears to be associated with MFS pending validation.
Presented by: Philip Sutera, MD, Johns Hopkins University, Baltimore, MD