PD-L1 expression on circulating tumor cells and CTC clusters as a minimal cellular disease in breast cancer patients.

e15036 Background: Tumor-transitioned components, for example, dual biomarkers like ctDNA and circulating tumor cells (CTCs) offer true comprehensive precision insights into tumor microenvironment in real-time. Importantly, minimal cellular residual disease (MCRD), dynamic cell surface protein over-expressions, residual burden measure post-resection with curative intent, adjunct therapy decisions, therapy de-escalations, etc. Like the PD-L1 % CPS score on tissues, the PD-L1 expression measure on CTCs is a higher prospect accounting for epithelial to mesenchymal transitions (EMT), leading to the deactivation of T Cells that may deactivate immune T cells further imparting micro-metastasis cascade is extremely challenging. We report the expression of PD-L1 as a dynamic biomarker on circulating tumor cells across early to late-stage breast cancer patients. Methods: In retrospective analysis, 1294 breast cancer patient’s peripheral blood was analyzed for the presence of CTCs with and without the expression of PD-L1 and CTC clusters. CTCs were enumerated using the OncoDiscover platform approved by CDSCO-India in 1.5 ml peripheral blood, consisting of multi-component magneto-nanosystem mediated by anti-epithelial cellular adhesion molecule (EpCAM) antibody. CTCs were positive with EpCAM +ve, CK18 +ve, DAPI +ve, and CD45-ve. Additionally, PD-L1 expression on the CTCs was measured based on the linear intensity gradients of the fluorescence signals using image acquisition on an automated Zeiss microscope. Further, we developed a computational model to account for CTC mean distribution, regression analysis, and predictability of CTC numbers. Results: The CTC distribution ranged from 1-20 CTCs, per 1.5 ml of patients’ blood. At baseline sample analysis, 73.20% (n = 978) of the patients showed ≥1CTCs. Whereas, 87.69% (n = 406 out of 463) of patients with CTCs showed the expression of PD-L1. Noteworthy, the highest number of CTC was observed at ~21.61% (n = 1125) in the age group 41-50, while the highest number of CTC clusters and CTC with PD-L1 was observed at ~29.08% (n = 41) and ~42.91% (n = 324) in the age group 51-60. Interestingly, 2.71% (n = 141) of total patients showed the presence of CTC clusters. The mean CTC (including clusters) and CTC with PD-L1 are 3.90 and 3.40, respectively. Further, the computational model showed a co-relation of blood-based outcome versus normal probability scores. Conclusions: The notable inter-patient heterogeneity suggests a potential biological, pharmacodynamic, role for both CTC with PD-L1 expression. The larger clinical studies are desired to evaluate PD-L1 expression of CTCs in early-stage cancers. Thus patients possessing MCRD despite the absence of radiographical evidence for stratifying them with a higher risk of metastasis progression.