Detection and Characterisation of Circulating Tumour Cell Clusters in Neuroblastoma

Background: Neuroblastoma (NB) is the most common extracranial paediatric solid cancer, with a 50% survival rate for high-risk patients. Circulating tumour cells (CTCs) are malignant cells shed by the primary tumour and metastatic sites that circulate in the bloodstream. CTCs form clusters with themselves (homotypic) or other cell types (heterotypic). Objectives: To use previously generated ImageStreamX Imaging Flow Cytometer data from blood samples from 24 patients across all NB risk groups, to examine for the presence of CTC clusters. Methods: Immunofluorescence and brightfield morphology were used to identify clusters followed by analysis using IDEAS image analysis software. Results: The mean number of clusters detected per sample was 87 (range, 0-725). Of the clusters detected, 1967/2094 (93.9%) were heterotypic and only 127/2094 (6.1%) were homotypic and found in 6/24 patients. Interestingly, in 3/24 patients, at least one cluster (median, 2 and range, 1-18) was found, but no single CTCs were detected. Clusters mostly comprised two cells (62.8%), with the maximum number of cells in homotypic and heterotypic clusters being four and eight, respectively. Conclusions: These results highlight that imaging flow cytometry can be used to detect and characterise CTC clusters in peripheral blood samples from NB patients, leading to further research exploring the composition and role of CTC clusters in NB metastasis.