Abstract 6440: Circulating tumor cell detection and characterization with the novel RareScopeTM technology
Authors: Reddy Aswanth , Tannenbaum Susan , Tafas Triantafyllos 
Published: September 2020

Abstract
Circulating tumor cells (CTC) are released by tumors in blood and lymphatic systems and are responsible for the creation of metastasis. They reflect the intra-tumoral heterogeneity and often have different phenotypes comparing to the primary tumor. In Circulating Tumor Cell Liquid Biopsy (CTC-LB) testing, higher CTC numbers correlate with worse prognosis, confirmed by a sharp decline in progression-free survival in studies utilizing CellSearch® technology. Clinically available CTC-LBs (except for EPIC Sciences) utilize enrichment methods that introduce detection bias. Proof of CTC-LB clinical utility will lead to broader CTC-LB adoption in the cancer diagnostic market.
The RareScope (QCDx LLC, Farmington CT) is designed to scan all nucleated cells from a patient's blood sample for unbiased CTC detection and phenotypic characterization. Fluorescence Light Sheet Microscopy offers 3-dimensional visualization of immobilized, morphologically intact cells either live or fixed and selected target cells can be isolated for downstream genomic and expression analyses. Experimentation showed RareScope linearity for detection of cancer cells at frequencies expected for CTCs in breast cancer patient blood. Cells from the SK-BR-3 breast cancer cell line were spiked in the buffy coat from healthy donor blood and fluorescently immunostained for CD45 pan leucocyte, cytokeratins 7&8 (CK), EpCAM and counterstained with DAPI (4′,6-Diamidine-2′-phenylindole dihydrochloride). Four preparations for each dilution of 2, 10, 15, 30, 75 and 300 cancer cells per 106 normal cells were mixed with immobilization medium and scanned with the RareScope. Digitized, 3D-images of each preparation were reviewed by two scientists and cancer cells were identified as CD45-, CK+, EpCAM+, DAPI+ while blood cells as CD45+, CK-, EpCAM-, DAPI+. Results of scanning the six dilutions were as follows [Expected cells: mean ± SEM of observed cells], [2 : 1.6±0.25], [10 : 12.8±4.3], [15 : 15.7±2.7], [30 : 37.1±7.5], [75 : 87.4±1.9] and [300 : 290.4±20.6]. Linear regression analysis of scan results showed R2 correlation coefficient of 0.992. The RareScope will be utilized in the IRB approved, prospective CLINBREAC study at the UConn Cancer Center, starting in January 2020. Blood samples will be collected from early stage and metastatic breast cancer patients longitudinally over a period of 24 months after enrollment for an average of 12 samples per patient. All analyzed cells will be confirmed by 2 cytotechnologists and a clinical cytopathologist. The trial objectives are to enumerate and characterize CTCs, assess the timing of disappearance or persistence with treatment, co-evaluate with NGS results from the primary tumor and compare with results from the CellSearch test. In summary, we anticipate that the RareScope technology will prove to be a high precision CTC-LB to detect and characterize CTCs following confirmation from the CLINBREAC study.
Citation Format: Aswanth Reddy, Susan Tannenbaum, Triantafyllos Tafas. Circulating tumor cell detection and characterization with the novel RareScopeTM technology [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6440.