Abstract

Background

Prostate cancer (PC) detection remains challenging due to the limited specificity and sensitivity of current screening methods, including PSA testing. PSA testing does not reliably distinguish aggressive disease from indolent forms, often leading to overdiagnosis and overtreatment. Circulating tumor cells (CTCs), however, offer greater clinical value by providing real-time insights into tumor biology, disease progression, and treatment response. Unlike PSA, CTCs represent a dynamic biomarker reflecting systemic minimal cellular residual disease (MCRD), which can support monitoring and guide personalized prostate cancer management. In addition, the overexpression of PD-L1 on CTCs provides insight into immune evasion mechanisms and may have predictive and prognostic value in prostate cancer. In this study, we report the capture of CTCs, including PD-L1–positive cells and CTC clusters, in prostate cancer patients.

Methods

A retrospective analysis was conducted on 239 prostate cancer patients to evaluate the presence of PD-L1–positive CTCs and CTC clusters. The cohort included 216 (90.4%) baseline samples and 23 (9.6%) follow-up samples. CTCs were isolated using the CDSCO-approved OncoDiscover Test (India), which employs anti-EpCAM antibody–based immunomagnetic enrichment from 1.5 mL of blood. CTCs were identified as CK18⁺/DAPI⁺/CD45⁻ cells with PD-L1 expression and distinct morphology. Automated fluorescence imaging was used to quantify signal intensities and correlate them with clinicopathological parameters. Patients were stratified by age, and quantitative analyses of CTC positivity, PD-L1 expression, and CTC cluster frequency were performed.

Results

CTCs were detected in 173 patients (72.4%), while 66 patients (27.6%) were CTC-negative. Among 157 evaluable samples for PD-L1 expression, 131 (54.8%) were PD-L1 positive and 26 (10.9%) were negative. CTC clusters were observed in 19 patients (11%), while 154 patients (89%) exhibited only single CTCs. At baseline, CTCs were detectable in 70.4% of patients, increasing to 91.3% in follow-up samples. PD-L1–positive CTCs were observed in 52.3% of patients at baseline and 85.7% at follow-up. Additionally, PD-L1–positive CTC clusters increased from 10.5% at baseline to 13.1% at follow-up. The predominant age groups were 61–70 years (39.0%) and 71–80 years (39.9%), together comprising nearly 80% of the cohort. The mean distribution of CTC counts per patient was 1.14 for total CTCs, 0.95 for PD-L1–positive CTCs, and 0.12 for CTC clusters.

Conclusion

A high prevalence of CTCs and PD-L1 expression was observed among prostate cancer patients, particularly in older age groups. The detection of PD-L1–positive CTCs highlights the presence of confirmatory MCRD and circulating disease. Although the incidence of CTC clusters was relatively low, their presence may indicate more aggressive disease phenotypes.