Measure of minimal residual burden on circulating tumor cells with over-expression of programmed death-ligand 1 as a dynamic biomarker in patients with colorectal cancer.

e14553 Background: In stage III colorectal cancer (CRC) patients, the extent of oxaliplatin-combination as an adjuvant therapy is still undetermined. Approx. 25-50% Stage II-III CRC patients are known to develop recurrence and metastasis even after comprehensive treatment, attributed to occult disease and Minimal Residual Disease (MRD). Circulating Tumor Cells (CTCs) are bio-mechanistic extravasation source for micro-metastatic disease. CRC patients, with lower adjuvant therapy from 3 to 6 months are known to exhibit increased CTCs and positivity rate due to the emergence of resistant clones. Assays to detect CTCs and expression of Programmed Cell Death-Ligand 1 (PD-L1) as a dynamic biomarker simultaneously has wide clinical implications. Especially, when the tissue biopsy is not inadequate to detect molecular targets for immune checkpoint inhibitor (ICT) therapy. Methods: Retrospectively, 182 CRC cancer patients were analyzed for the presence of CTC and distribution at baseline and follow-ups (up to 0-4 follow ups). The peripheral blood 1.5 ml was analyzed using the OncoDiscover platform approved by CDSCO, India consisting multifunctional magneto-nanosystem mediated by anti-epithelial cellular adhesion molecule (EpCAM) antibody. CTCs were analyzed in patients with early stages- pre and post treatment, progressive disease, Disease Free Status (DFS) and in metastasis. The isolated cells were immune-stained to detect CK-18 +ve, CD45 -ve, DAPI +ve and PD-L1 +ve expression. PD-L1 expression in CTCs was validated by analyzing the linear intensity gradients of the fluorescence signals. CTCs were termed as PD-L1 -ve based on a weak or no detectable fluorescence signal and termed +ve based on a high fluorescence signal using automated image acquisition Zeiss microscope. Results: In a cohort of 182 CRC patient samples, n = 128 (70.3 %) showed the presence of CTCs. The fluorescence intensity for PD-L1 expression as a robust functional assay on CTCs for molecular characterization was developed. The distribution of CTCs ranged from 1-9. The mean fluorescence intensity value and cut-off for the expression of PD-L1 in CTCs was accounted to be ~1.02. Interestingly, in n = 54 (42.2 %) patients, CTCs showed positive expression of PD-L1. CTC +ve patients with PD-L1 expression were associated at all stages and even in early stage, progressive disease, and metastasis. Patients without any CTCs n = 54 (29.7%) either had clinically stable disease or were in DFS with no radio-graphical image. Conclusions: The presence of PD-L1 over-expression on CTCs is a dynamic biomarker in blood, showing the progression of disease even in patients with DFS status. CTC enumeration and assessing the PD-L1 expression on CTCs could offer highly individualized treatment plans in CRC patients.