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Title: Effectively sampling rectal mucus and assessing the validity of a DNA methylation assay in the detection of colorectal cancer
Author: Tzivanakis, Alexios
ISNI:       0000 0004 5358 8637
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2014
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Colorectal cancer (CRC) is one of the most common cancers in the Western world. Screening for CRC using faecal occult blood test (FOBT) is well established. There is evidence that DNA based stool tests may be more effective than FOBT. Hypothesis The hypothesis is that in patients with CRC, rectal mucus may contain DNA derived from colonic tumours. It is speculated that quantitative or qualitative assessment of DNA in rectal mucus may permit an improved method of CRC screening. Aims Using surgically resected specimens of colonic tumours: To assess the feasibility and reliability of measuring DNA in mucus samples To compare different devices to measure mucus DNA To assess the amount of mucus DNA at various distances from colonic tumours In patients with CRC and controls: To compare the amount of DNA in rectal mucus Using a panel of 3 DNA methylation markers, to compare the rectal mucus DNA methylation profile between patients with CRC and controls Methods Surgical colectomy specimens were obtained from 25 patients with CRC. The feasibility and repeatability of measuring mucus DNA amounts was established using different buffer solutions, different storage techniques and different sampling devices. Mucus DNA amounts were measured at tumour sites and various distances proximal and distal to the tumour. 58 patients referred to a colorectal outpatient clinic with suspected CRC were assessed. Rectal mucus samples were obtained using a balloon device introduced through a proctoscope. All patients were investigated by colonoscopy to clarify the presence or absence of a CRC. The amount of DNA in the mucus samples was measured. The presence of three DNA methylation markers (NDRG4, TFP12 and GATA4) was assessed in all samples. All studies were approved by the local ethics committee. Results Reliable measurement of DNA from mucus samples was established using balloon, foam and brush devices and a cell lysate buffer. Higher amounts of DNA in surgical specimens were found distal to tumours compared to proximally. In patients with CRC the amount of DNA in rectal mucus was higher than in controls (no disease or benign polyps). The three DNA methylation marker panel had a sensitivity of 87% and specificity of 27.5% for the detection of CRC. Conclusions The results are consistent with the hypothesis that DNA detected in rectal mucus is derived from proximal tumours. Higher levels of rectal mucus DNA are obtained from patients with CRC than from controls. The selected DNA methylation panel was not sufficiently useful in our sample group to be of use as a screening technique, due to poor specificity. Further work is in progress to compare DNA abnormalities in resected tumour tissue with DNA from rectal mucus in the same patients. Future work may be required to improve the panel of DNA abnormalities assessed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: RC0254 Neoplasms. Tumors. Oncology (including Cancer)