Efficacy of VELscopeTM in clinical practice: Clinical and pathological correlations

Abstract

Oral cancer is most commonly referred to as cancer of the lip, oral cavity and oropharynx with 90% of oral malignancies being attributed to oral squamous cell carcinomas (OSCC). It is estimated that 263, 900 new cases are diagnosed worldwide per year with 128,000 deaths being attributed to OSCC in 2008 alone. The survival rate has remained unchanged for last three decades at around 50%, largely due to the delayed diagnosis of these cancers. Additionally, OSCC are often preceded by changes to the oral mucosa which can be detected on visual examination. Lesions which have the propensity to progress to malignancy are referred to as oral potentially malignant disorders (OPMD). Therefore, to improve patient outcomes there has been increased emphasis on detecting OSCC and OPMD at an earlier stage, New technologies which assist lesion visualisation have been made available to assist the general and specialist practitioner in detecting OPMD, and also differentiating OPMD from benign lesions. This thesis will focus on VELscopeTM, a device which utilises direct tissue autofluorescence to perform this function. When visualised with VELscopeTM, normal mucosa is associated with a pale green autofluorescence, while abnormal mucosa is associated with loss of autofluorescence (LAF). It is well reported in the literature that VELscopeTM is associated with high sensitivity for the detection of dysplasia but low specificity, and there are concerns regarding the presence of false positives due to inflammatory lesions also displaying LAF. In specialist practice, the device is effective in detecting dysplasia however it can be difficult to distinguish dysplasia from benign inflammatory lesions. Diascopic fluorescence, when the lesion returns to a normal fluorescence pattern under pressure, can help discern inflammatory lesions from those with malignant potential. Additionally, some cases of dysplasia may not display LAF. In general practice, the literature is limited however the main concerns are that relying on VELscopeTM alone may lead to gross over referrals. This thesis looks at addressing some of the concerns associated with the use of VELscopeTM in clinical practice to allow for greater uptake of this technology by both general and specialist practitioners. This thesis is divided into three discrete chapters. The first chapter reviews the literature regarding OPMDs and the various technologies available to assist in their earlier detection, and includes some literature regarding future developments in this area.The second chapter is an experimental chapter which investigates methods to utilise VELscopeTM for routine screening of patients in general dental practice. Patients presenting to the University of Queensland School of Dentistry were screened by a general dental practitioner utilising a decision making protocol whereby patients were first screened using conventional oral examination (COE) under incandescent light, followed by VELscopeTM and then by correlating the findings from these two examinations. In total, 305 patients were screened over a 19 month period. Using the decision making protocol proposed in this study and by incorporating VELscopeTM into general dental practice allows for the detection of oral mucosal lesions requiring specialist referral without compromising patient care. To elucidate why some OPMD were associated with LAF, while other lesions with similar histology were not, the third chapter discusses potential underlying molecular mechanisms regarding LAF. Forty-three frozen tissue samples from archival material were correlated with clinical data regarding fluorescence characteristics. Relative gene expression was measured using Next Generation Sequencing (NGS) RNA-Seq and correlated with the clinical phenotype. No unifying genes related to LAF were identified. In dysplasia, LAF was associated with angiogenesis while blanching was related to inflammation. In keratosis/hyperplasia LAF was associated with cell proliferation and apoptosis while again blanching was related to inflammation. Biological causes for LAF were different between different histological groups but are associated with pathways related to angiogenesis, inflammation and cell cycle deregulation. This thesis demonstrates the utility of VELscopeTM in clinical practice, and how it can be effectively used in a general practice environment. Additionally, by uncovering molecular mechanisms underlying LAF, it is envisaged that further research can translate this into the clinical environment to reduce the rate of false positives and negatives allowing for more widespread use of VELscopeTM for the detection of OPMD.