Effect of circulating tumor cells (CTC) and CTC clusters with PD-L1 dynamic biomarker on cellular burden in patients with ovarian cancer.

Abstract

e17566 Background: In the precision oncology era, monitoring response to the treatments using circulating blood-based biomarkers e.g. circulating tumor DNA (ctDNA) and Circulating Tumor Cells (CTCs) are being rapidly evaluated and established. The leading cause of ovarian cancer patient mortality is owing to the delayed diagnosis, inability of patient selection for targeted therapies, including the use of immune checkpoint blockade (ICB) agents. The treatment of ovarian cancer usually involves a combination of surgery and chemotherapy. However, post operative resection and therapy with curative intent often fails in accounting the Minimal Cellular Disease (MCD). The dissemination of Circulating Tumor Cells (CTC) remains a dogma of Minimal Residual Disease (MRD) that diffuse and cause micro-metastasis through their epithelial to mesenchymal transitions (EMT) and ‘bio-mechanistic activation’ in blood circulation. Simultaneous detection of over-expression of Programmed Cell Death-Ligand 1 (PD-L1) on CTCs as a dynamic biomarker may be expedient for assessing patients for immune checkpoint inhibitor (ICT) therapy. Methods: In retrospective analysis of real-world data, 75 ovarian cancer patient’s peripheral blood was analyzed for the presence of CTCs with and without the expression of PD-L1 and CTC clusters. CTC were positively detected using OncoDiscover platform approved by CDSCO in 1.5 ml peripheral blood. The platform is multifunctional magneto nanosystem mediated by anti-epithelial cellular adhesion molecule (EpCAM) antibody. CTCs were identified as positive if they were EpCAM +ve, CK+ve, PD-L1 +ve, DAPI +ve and CD45-ve. PD-L1 expression on the CTCs was analyzed based on the linear intensity gradients of the fluorescence signals using image acquisition on an automated Zeiss Microscope. Results: At baseline sample analysis, 86 % (n=65) of the patients showed ≥ 1CTCs per 1.5 ml of blood. The CTC distribution in this study ranged from 1-9 CTCs. Whereas, 46.15 % (n=30) patients with CTCs showed the expression of PD-L1. Noteworthy, the highest number of CTCs were observed ~ 26.7 % (n=23) in age group 41-50. Interestingly, 8 % (n=6) of total patients showed the presence of CTC clusters. The presence of CTCs with expression of PD-L1 and CTC clusters did not correlate with factors like staging, follow ups, metastasis, and DFS status. Conclusions: We observed presence of MCD and MRD in CRC patients, in spite of curative intent in ovarian cancers. Detection of CTCs, CTC clusters with over-expression of PD-L1- as a real time dynamic biomarker may be useful for assessing the patients for early metastasis, regression, and selecting patient suitable for immune checkpoint inhibitor (ICT) therapy when the tissue is inadequate or unavailable for better outcome.