Detection of PSMA expression on circulating tumor cells by blood-based liquid biopsy in prostate cancer

Area of Science:

• Oncology
• Molecular Diagnostics
• Genomics

Background:

• Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy improves outcomes for metastatic castration-resistant prostate cancer (mCRPC).
• Identifying patients likely to benefit from PSMA-targeted therapy is crucial for treatment optimization.
• A liquid biopsy assay for PSMA expression on circulating tumor cells (CTCs) could enhance therapeutic decision-making.

Purpose of the Study:

• To develop and validate a blood-based liquid biopsy assay for detecting PSMA protein expression on CTCs.
• To assess the assay's analytical performance and clinical utility in mCRPC patients.

Main Methods:

• A four-color immunofluorescence (IF) assay using high-throughput imaging and AI pathology was developed to detect PSMA on CTCs.
• Analytical validation involved cell lines spiked into blood to determine precision, specificity, sensitivity, and accuracy.
• Clinical validation was performed on 24 PSMA-PET-positive mCRPC patients using 3 mL of blood, including low-pass whole-genome sequencing of CTCs.

Main Results:

• The PSMA CTC IF assay demonstrated analytical specificity, sensitivity, and accuracy exceeding 99% with high precision.
• Clinical validation showed 76% of cases were PSMA-positive with CTC heterogeneity, and 88% of patients had at least one CTC per milliliter.
• Sequenced CTCs frequently showed copy number alterations in genes like AR, MYC, RB1, PTEN, TP53, and BRCA2.

Conclusions:

• The liquid biopsy CTC platform effectively detects PSMA protein expression in mCRPC patients' CTCs.
• This assay serves as a valuable research tool for evaluating PSMA expression, heterogeneity, and treatment response in ongoing clinical studies targeting PSMA-expressing tumors.