Molecular prognostic markers in renal cell carcinoma
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Renal cell carcinoma (RCC) is the most deadly of urological malignancies. While metastatic disease affects one third of patients at diagnosis, a further third of patients who undergo extirpative surgery with curative intent subsequently develop metastatic disease. Inconsistency in the clinical course ensures predicting subsequent metastasis is notoriously difficult, despite the routine use of prognostic clinico-pathological parameters in risk stratification. With greater understanding of pathways involved in disease pathogenesis, a number of biomarkers have been proposed to be of prognostic significance; however there are currently no molecular prognostic markers in clinical use. Genetic intra-tumoural heterogeneity (genetic ITH) has been described in clear cell RCC (ccRCC) and may limit the clinical translation of biomarkers. There has been no assessment of ITH at other molecular levels. The aim of this work was to define and compare proteomic, transcriptomic and DNA methylation ITH in ccRCC, and identify potential prognostic biomarkers. Using reverse phase protein arrays to study protein expression in multiple spatially separate regions of primary and metastatic ccRCC, proteomic ITH was demonstrated for the first time. Interestingly there was no significant difference in proteomic ITH in metastatic ccRCC tumour deposits compared to primary tumours. However, on analysis of differential protein expression between primary and metastatic ccRCC tissue using a tissue microarray and automated analysis of immunofluorescence, there was significantly greater expression of Ki67, p53, VEGFR1, SLUG and SNAIL in the metastases compared to the primary tumours. Subsequent profiling of gene expression and DNA methylation in multiple areas of the same primary tumours confirmed transcriptomic and methylomic ITH. On comparison of this multimolecular ITH, significantly greater proteomic ITH was seen compared to gene expression and DNA promoter methylation heterogeneity. Recent evidence suggests DNA methylation may be prognostically important in RCC and given the lower methylomic ITH in ccRCC, the identification of prognostic DNA methylation changes in ccRCC were pursued using the Infinium HumanMethylation450K Beadchip. Following development of an analysis pipeline, identification and validation of prognostic differentially methylated regions (DMR) was performed on an experimental cohort and published dataset respectively. Five DMRs, which were associated with disease recurrence in ccRCC, were identified. NEFM gene promoter methylation was the only DMR associated with cancer specific survival, independent of TNM stage and nuclear grade on multivariate analysis, which was confirmed on a third independent published dataset. This thesis therefore demonstrates multi-molecular ITH in ccRCC for the first time. Despite this, NEFM promoter methylation may be a useful independent prognostic marker of cancer specific survival.