Abstract 1079: Over expressing PD-L1 circulating tumor cells with clusters in prostate cancer patients

Abstract Background: Prostate cancer (PC) detection remains challenging due to the limited specificity and sensitivity of current screening methods, including PSA testing. However doesn’t distinguish aggressiveness from indolent disease, leading to overdiagnosis and overtreatment. Circulating Tumor Cells (CTCs), however, offer greater clinical value as they provide real-time insights into tumor biology, disease progression, and treatment response. Unlike PSA, CTCs represents a dynamic biomarker implicating minimal cellular residual disease (MCRD) systemically, helpful for monitoring and guiding the personalized prostate cancer management. In addition, the over- expression of PD-L1 on CTCs provides insights into immune evasion mechanisms and may have predictive and prognostic value in PC. We report CTC capture, having PD-L1 positivity and clusters, in PC patients. Methods: Retrospectively, 239 prostate cancer patients were analysed for presence of CTC-PD-L1 and CTC clusters, including 216 (90.4%) baseline and 23 (9.6%) follow-up samples. CTCs were isolated using the CDSCO-approved (India) OncoDiscover Test employing anti EpCAM antibody-based immunomagnetic enrichment / 1.5 ml of blood. CTCs were identified as CK18+/DAPI+/CD45-, PD-L1 expression+ cells with distinct morphology. Automated fluorescence imaging quantified signal intensities to correlate with clinicopathological parameters. Patients were stratified for age, and quantitative analysis of CTC positivity, PD-L1 expression, and cluster frequency was performed. Results: CTCs were detected in 173 (72.4%) patients, while 66 (27.6%) were negative. Amongst 157 evaluable samples for PD-L1, 131 (54.8%) were PD-L1 positive and 26 (10.9%) were negative. CTC clusters were observed in 19 (11%) patients, while 154 patients (89%) had only single CTCs. At baseline, CTCs were detectable in 70.4% of patients, increased to 91.3% at follow-up patients. While, CTC-PD-L1 positivity was observed in 52.3% patients at baseline and 85.7% in 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 were 1.14, 0.95 for CTCs with PD-L1, 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 +ve CTCs highlights the presence of confirmative MCRD, and presence of disease in circulation. The relatively low incidence of CTC clusters suggests limited collective migration, although their presence may signify more aggressive disease phenotypes. Citation Format: Jayant Khandare, Bharat Bhosale, Gourishankar Aland, Sreeja Jayant, Amrut Ashturkar, Vikas Jadhav, Ashish Joshi, Sourav Mishra, Pradip Kendre, Aravindan Vasudevan, Vashishth Maniar, Jagdeesh Kulkarni. Over expressing PD-L1 circulating tumor cells with clusters in prostate cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1079.