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Title: Identification of markers for relapse and candidate genes for involvement in the progression of stage I non-seminomatous testicular germ cell tumours
Author: Gilbert, Duncan
ISNI:       0000 0004 2710 4424
Awarding Body: Institute of Cancer Research (University Of London)
Current Institution: Institute of Cancer Research
Date of Award: 2009
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Testicular germ cell tumours (TGCT) are the commonest solid tumour to affect young adult males and are increasing in incidence for reasons poorly understood. 60% of the non-seminomatous (NS) subtype present with stage I disease (clinically localised to the testes). Although apparently cured by surgery alone, up to 50% will subsequently relapse through the presence of micrometastases. Adjuvant chemotherapy reduces the relapse rate to 2%, but is associated with acute toxicity and long-term side effects (second cancers and an increased risk of cardiovascular disease) and represents unnecessary treatment for at least half of these patients. Histological evidence for vascular invasion is currently used as an indicator of subsequent relapse but is inaccurate and therefore improved prognostic markers are urgently required. In order to identify genomic regions associated with likelihood of relapse, full tiling path resolution BAC array comparative genomic hybridisation was used to characterise formalin fixed, paraffin embedded material from 32 stage I NS, 15 of which were known to subsequently relapse. Published expression microarray data from TGCT was then used to identify gene expression patterns from the genomic regions identified. This identified candidate genes as markers of relapse as well as supporting the importance of RAS and PI3 kinase signalling in TGCT. In addition, the expression levels of known mediators of metastatic dissemination were identified as further candidates for involvement in TGCTs. Genomic data demonstrated loss of 22q12.2 (containing DRG1 and PIK3Ip1) and gain of 22q13.32 (BRD1) being associated with relapse and a cluster of cytokines on 17q12 associated with vascular invasion. These genes were investigated using immunohistochemistry on a tissue microarray constructed from 83 stage I NS with known clinical outcomes. Candidates selected on the basis of the expression data and their potential functional role were VEGF-A, MMP2, MMP9 and the chemokine CXCL12 and its receptor CXCR4. Variable rates of expression of VEGF-A, MMP2 and MMP9 were identified though no correlations with subsequent clinical behaviour found. Universal expression of the chemokine receptor CXCR4 by TGCT was demonstrated, with autocrine expression of the ligand CXCL12 associated with a reduced rate of subsequent relapse (p=0.003) indicative of a significant prognostic marker. This could be explained by low intratumoural expression of CXCL12 mediating migratory behaviour. Consistent with this hypothesis, functional work using TGCT cell lines demonstrated CXCR4 mediated migration towards CXCL12 gradients, with concurrent activation of ERK1/2. Based on this study, work to validate CXCL12 as a clinically useful prognostic marker in stage I NS is warranted and currently underway using samples from patients treated and monitored in a clinical trial setting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available