(UroToday.com) The 2023 GU ASCO annual meeting included a session on prostate cancer, featuring a presentation by Dr. Baris Esen discussing 68GaPSMA-11 PET/CT to monitor treatment response in patients with metastatic prostate cancer. Data about the role of PSMA PET to monitor treatment response is scarce in the literature. The aim of this study was to assess whether PSMA PET is associated with flares, with discordant results in regard to biochemical response, and with positivity rates at low PSA values while monitoring metastatic prostate cancer receiving systemic treatment.
A total of 96 patients with PSMA PET-detected metastatic prostate cancer who underwent at least one follow-up scan after receiving systemic treatment were included in the study. PSA levels at baseline PSMA PET-CT and follow-up PSMA PET scans were recorded. Any significant PSMA uptake at prostate and/or metastatic lesions were considered PSMA positive. PSMA response were decided according to PSMA PET progression criteria. Biochemical progression was defined as ≥25% increase in PSA (1 ng/dL was the minimal starting value). Additionally, PSMA PET and PSA response were dichotomized into progressive disease vs non-progressive disease. Discordant responses among different metastases and prostate were defined as the condition when some metastatic lesions (or prostate) are responding (complete response or partial response) to systemic treatment while others had progressed.
A total of 345 serial PSMA PET/CT (96 baseline PSMA PET-CT and 249 follow-up PSMA PET) scans were evaluated. The median time between consecutive PSMA PET scans was 6.3 months (IQR 4.7 – 10.6) Overall PSMA PET positivity rate of follow-up PSMA PET scans was 88.4% (220/249). The following table demonstrates PSMA PET positivity rates according PSA values:
PSMA PET progression was detected in 93 cases (37.8%) and biochemical progression was observed in 73 cases (30.2%). PSA and PSMA responses were highly concordant (Cohen’s K=0.623, p<0.001). PSA-PSMA discordant responses were detected in 39 scans (17%). The possible causes could be identified in 34 of 39 scans (87%) while no obvious reason for discordance could be shown in the remaining five cases:
The most common cause of discordance was discordant responses between different metastatic sites to systemic treatment:
Dr. Esen concluded his presentation discussing 68GaPSMA-11 PET/CT to monitor treatment response in patients with metastatic prostate cancer with the following concluding messages:
- PSMA PET/CT showed very high detection rates of malignant lesions even in very low PSA values when monitoring treatment response in patients receiving systemic treatment for metastatic prostate cancer
- PSA and PSMA responses were highly concordant. In cases with discordance, the reason seems to be the discordant behaviour of intraprostatic and metastatic lesions and not necessarily PSMA flares
- PSMA PET is a promising biomarker to assess treatment response in patients with metastatic prostate cancer
Presented by: Baris Esen, MD, PhD, FEBU, MSc, Koc University School of Medicine, Department of Urology, Istanbul, Turkey
Co-Authors: Hulya Seymen, Kayhan Tarim, Ersin Köseoğlu, Yasemin Bolukbasi, Okan Falay, Mehmet Onur Demirkol, Derya Tilki, Tarik Esen
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2023 Genitourinary (GU) American Society of Clinical Oncology (ASCO) Annual Meeting, San Francisco, Thurs, Feb 16 – Sat, Feb 18, 2023.