Evaluating cellular microRNA expression in human papillomavirus associated head and neck squamous cell carcinoma

Abstract

Squamous cell carcinoma of mucosal head and neck sites (HNSCC) is the sixth most common cause of cancer world-wide, and is associated with a significant morbidity and mortality despite advances in therapeutic options over the past decades. HNSCC includes tumours of the oral cavity, oropharynx, larynx and hypopharynx. While there has been a decline in tumours occurring as a result of exposure to the traditional risk factors of tobacco smoking and alcohol consumption, a significant increase has been observed in the number of tumours attributed to the Human Papillomavirus (HPV). This has primarily been associated with causation of tumours in the oropharynx, however, a smaller number of tumours at other subsites are also likely to be related to the virus. Although HPV-related tumours tend to have an improved prognosis and a better response to chemo-and radiotherapy, the pathobiology underlying these differences is not yet fully understood.MiRNAs are short, non-coding single strands of RNA which regulate gene expression at the posttranscriptional level. They have been identified to be dysregulated and function as tumour suppressor or oncogenes in a number of human cancers, including head and neck cancers. MiRNAs have also been associated with prognostication including associations with recurrence of disease and diseasefree survival. As they are readily available across a range of body tissues including solid tissue, saliva, and plasma, these biomarkers have potential utility in relation to screening for disease diagnosis, recurrence or progression. Although there is an established difference between HPV-positive and negative tumours in the oropharynx clinically, the majority of studies investigating miRNA expression in HNSCC have not taken this factor into account. In the small number of studies which have examined the effect of HPV on miRNA expression in HNSCC, there is a lack of consistency in the results described.This thesis aimed to assess the difference in miRNA expression between HPV-positive and negative tumours, through use of miRNA microarray followed by validation with real-time PCR using TaqMan assays combined with a sensitive detection method (Fluidigm HD) in a larger cohort of patients. It also investigated differences in miRNA expression in association with lifestyle factors, demographics and clinical outcomes. A set of seven miRNAs was identified to be differentially expressed between HPV-positive and negative tumours in the oropharynx. No difference in miRNA expression was observed between the two tumour cohorts at other subsites in the head and neck.Differences in miRNA expression were also observed with lifestyle factors such as smoking status and alcohol consumption. Recurrence of the primary tumour and overall disease-free survival were further associated with altered miRNA expression. The findings outlined in this thesis add to the present literature regarding differences in miRNA expression between HPV-positive and negative iii tumours in the oropharynx, and provide a basis for further...