title: Circulating Tumour Cells in Oral Squamous Cell Carcinoma: Characterisation and Kinetics during the Peri-operative Period
Creators: name: Curtin, Justin
Publisher: name: Griffith University
Year: 2024
Subjects: subject: oral cancer
subject: circulating tumour cells
subject: anaesthesia

description: Circulating malignant cells (CMCs) are cancer cells released by a primary cancer into peripheral circulation. There is level 1 evidence that the presence of CTCs is prognostically relevant for adenocarcinomas arising from colorectal, prostate and breast tissue. Yet little is known of their significance in oral squamous cell carcinoma (OSCC). The malignant nature of cells isolated in peripheral blood samples can now be confirmed using in situ functional hybridisation to identify chromosomal aneuploidy. Epithelial, mesenchymal and endothelial molecular markers enable mesenchymally transformed epithelial cells to be detected and differentiated from circulating endothelial calls. Automated image analysis is used to differentiate between single CMCs and clusters of CMCs. By these means, an extended range of CMCs has been identified that includes single circulating tumour cells (CTCs), circulating tumour microemboli (CTM, also called "clusters") and circulating tumour endothelial cells (CTECs). To date, almost all investigations have focused on CMCs in adenocarcinoma, a disease markedly different to OSCC. Such studies have produced biologically based insights now directly translated into clinical practice to dramatically improve patient outcomes. Although OSCC is ranked sixth for global incidence, in Asia it ranks within the top three cancer presentations. Astounding advances in surgical methods and adjunctive therapies have enabled treatment of tumours previously deemed inoperable, and yet despite these advances, survival for persons with OSCC has improved little in recent decades. Again in contrast to adenocarcinoma, current understanding of the biology of OSCC is limited. This threshold of understanding is reflected in the absence of an effective biomarker able to detect early disseminated disease or monitor progress. Limited understanding of the underlying metabolic and phenotypic traits of OSCC are also limits the use of targeted therapies or the identification of 'at risk' individuals. With the long-term goal of addressing these limitations, this project had the following objectives: 1. To review current knowledge regarding CMCs in OSCC. 2. To determine the optimal physically based method of CMC isolation. 3. To measure the numbers of CMCs and CMC sub-types in patients with OSCC over the peri-operative period and influence of treatment on CTC numbers. These aims were achieved in three stages: 1. Reviewing the current literature to determine the reported incidence of circulating malignant cells in persons with OSCC. 2. By comparison of two physically based methods of CMC isolation and determining the superior method of CMC detection to be used in the observational clinical investigation. 3. Undertaking a clinical observational investigation of patients with OSCC that measured the numbers of CMC and CMC sub-types pre-operatively (baseline), immediately upon tumour removal and post-operative day one and day seven. This led to the following findings: 1. The current literature pertaining to CMCs in OSCC is sparse, with only twenty-two studies meeting the selected inclusion criteria. 2. That using filtration (ISET®) to isolate CMCs that arise from OSCC is the suboptimal method when compared to a microfluidic method (Cytelligen®). Filtration isolation failed to identify circulating tumour micro-emboli ("clusters") and is unable to identify CTECs. 3. That in persons with OSCC the presence of CMCs occurs independently of TNM staging. 4. The relative distribution of CTCs, CTMs and CTECs between participants occurs in an apparently idiosyncratic manner. 5. The CMCs were present in the majority of patients tested. 6. CMCs were detected in all participants at some time point during the peri-operative period. 7. CTC numbers changed over time under the influence of surgical manipulation. There were statistically significant increases in CTC and CTM numbers upon tumour removal. The numbers of CTEC were not significantly impacted by tumour removal. 8. Although no overall trends were detected in the numbers of CMCs, CTCs, CTMs and CTECs persisted in the majority of participants on post-operative day seven. This study shows that CMCs are present in the majority of persons with OSCC independently of tumour staging and that persist despite complete tumour removal. These findings suggest that haematogenous systemic spread of OSCC occurs in an apparently idiosyncratic manner. While the prognostic significance of these findings requires long term follow-up of the participating cohort, this study supports the proposition that further investigations into CMCs in OSCC offers the potential to reveal biological insights to improve prognostication and discovery of biologically targeted therapies.