RareCyte® CTC Analysis Step 3: Using the CytePicker® Module for Individual Cell Retrieval and Subsequent Whole Genome Amplification of Circulating Tumor Cells for Genomic Analysis

Clinical Validation of a Circulating Tumor Cell Assay Using Density Centrifugation and Automated Immunofluorescence Microscopy

OBJECTIVES

The US Food and Drug Administration (FDA)-approved CELLSEARCH assay (Menarini Silicon Biosystems) for circulating tumor cells (CTCs) relies on expression of an epithelial cell adhesion molecule to enrich for CTCs. We sought to validate a CTC assay (RareCyte) for clinical use that instead collects a buffy coat preparation enriched for CTCs.

METHODS

Normal peripheral blood specimens spiked with cultured breast and prostate cancer cells and 47 clinical samples were used to validate assay performance. Specimens were enriched for buffy coat cells and applied onto 8 glass slides. The slides were immunofluorescently stained and imaged by automated microscopy and computer-aided image analysis.

RESULTS

The assay was 100% specific for detecting spiked tumor cells. For samples spiked with 25, 50, and 125 cells, the percentage coefficients of variation were 42%, 21%, and 3.7%, respectively. Linearity studies demonstrated a slope of 0.99, an intercept of 1.6, and R2 of 0.96. Recoveries at the 25-, 50-, and 125-cell levels were 92%, 111%, and 100%, respectively. Clinical samples run on both CELLSEARCH and RareCyte correlated with an R2 of 0.8 after log-transformation and demonstrated 87.5% concordance using the CELLSEARCH criteria for predicting adverse outcomes.

CONCLUSIONS

The RareCyte CTC assay has comparable performance to the FDA-cleared method and is ready for further clinical validation studies.

Applications of liquid biopsy in the Pharmacological Audit Trail for anticancer drug development

Anticancer drug development is a costly and protracted activity, and failure at late phases of clinical testing is common. We have previously proposed the Pharmacological Audit Trail (PhAT) intended to improve the efficiency of drug development, with a focus on the use of tumour tissue-based biomarkers. Blood-based 'liquid biopsy' approaches, such as targeted or whole-genome sequencing studies of plasma circulating cell-free tumour DNA (ctDNA) and circulating tumour cells (CTCs), are of increasing relevance to this drug development paradigm. Liquid biopsy assays can provide quantitative and qualitative data on prognostic, predictive, pharmacodynamic and clinical response biomarkers, and can also enable the characterization of disease evolution and resistance mechanisms. In this Perspective, we examine the promise of integrating liquid biopsy analyses into the PhAT, focusing on the current evidence, advances, limitations and challenges. We emphasize the continued importance of analytical validation and clinical qualification of circulating tumour biomarkers through prospective clinical trials.

The RareCyte® platform for next-generation analysis of circulating tumor cells

Circulating tumor cells (CTCs) can reliably be identified in cancer patients and are associated with clinical outcome. Next-generation "liquid biopsy" technologies will expand CTC diagnostic investigation to include phenotypic characterization and single-cell molecular analysis. We describe here a rare cell analysis platform designed to comprehensively collect and identify CTCs, enable multi-parameter assessment of individual CTCs, and retrieve single cells for molecular analysis. The platform has the following four integrated components: 1) density-based separation of the CTC-containing blood fraction and sample deposition onto microscope slides; 2) automated multiparameter fluorescence staining; 3) image scanning, analysis, and review; and 4) mechanical CTC retrieval. The open platform utilizes six fluorescence channels, of which four channels are used to identify CTC and two channels are available for investigational biomarkers; a prototype assay that allows three investigational biomarker channels has been developed. Single-cell retrieval from fixed slides is compatible with whole genome amplification methods for genomic analysis. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.