Author: Wong, Hung Lai
Title: Detection of driver mutations, particularly KRAS exon 2 in CD166-positive colorectal carcinoma and adenoma cells
Advisors: Wong, S. C. Cesar (HTI)
Degree: DHSc
Year: 2019
Subject: Hong Kong Polytechnic University -- Dissertations
Colon (Anatomy) -- Cancer -- Genetic aspects
Rectum -- Cancer -- Genetic aspects
Department: Faculty of Health and Social Sciences
Pages: xii, 86 pages : color illustrations
Language: English
Abstract: Background and Objective: Colorectal cancer (CRC), the third most common malignancy worldwide, remains a significant cause of cancer-related mortality due primarily to recurrence and metastasis. The underlying culprit is widely considered as cancer stem cell (CSC) characterized by self-renewal that drives tumor initiation and progression, suggestive of origin of relapse and distant metastasis being post-surgery residual/drug resistant CSCs. Increasing evidence indicates that CSC phenotype is likely promoted by cooperation of multiple oncogene and tumor suppressor gene mutations, resulting in aggressive neoplastic behavior. We therefore speculated that in CRC, 1) CSC marker-positive cells may harbor more driver mutations than CSC marker-negative cells and 2) CSC marker-positive cells carrying those mutations may be identified as aggressive subpopulation and associated with poor prognosis. Accordingly, mutations in common driver genes -APC, BRAF, CTNNB1, KRAS, PIK3CA, FBXW7, SRC and TP5, particularly oncogenic KRAS in CSC marker, CD166-positive colorectal carcinoma and adenoma cells were studied to explore their potential use in diagnosis and prognosis of CRC. Materials and Methods: 42 respective CRC and colorectal adenoma (CAD) specimens were analyzed for CD166-positive tumor cells by immunohistochemistry followed by mutation profiling of aforementioned driver genes in macrodissected CD166-positive and -negative tumor cells using mutation PCR array. Among gene mutants, KRAS exon 2 mutations were further investigated in extended cohort of 70 CRC and 72 CAD specimens same as above approach, except mutation detection by Sanger sequencing. CD166 and KRAS mutation status were correlated with clinico-pathological parameters and post-treatment outcome of CRC patients. Results: The immunoreactivity of CD166 protein showed significant difference among CRC, CAD, and normal colorectal epithelial tissue (p < 0.0001, Kruskal-Wallis test) with increasing trend from normal tissue to CAD and CRC. Mutation profiling revealed that CD166 positive carcinoma or adenoma cells tended to carry greater percentage and wider spectrum of driver mutations than CD166 negative counterparts. Importantly, mutation frequency of KRAS exon 2 detected by sequencing was 1.8-fold significantly higher in CD166 positive CRC cells versus CD166 negative CRC cells (p < 0.05, chi-square test). Long term follow-up of the CRC patients demonstrated that concomitant KRAS mutation and CD166 expression in CRC cell was useful in discriminating poor post-treatment outcome. Conclusion: This study provided evidence of 1) higher KRAS exon 2 mutation frequency in CSC marker, CD166 positive CRC cells versus non-CSC marker, CD166 negative CRC cells, and 2) prognostic value of KRAS mutation in CD166 positive CRC cells in predicting worse patient outcome. These significant findings are worthwhile to be verified in a large scale study for translating into clinical applications of CRC.
Rights: All rights reserved
Access: restricted access

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