3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Analysis of radiosensitivity in South African cervical and breast cancer patients(2015) Herd, Olivia JayneIntroduction: Ionising radiation can cause DNA double strand breaks (DSB), that result in chromosomal aberrations if un- or mis-repaired. Individuals with compromised DNA damage repair mechanisms display increased chromosomal radiosensitivity. The G0-micronucleus assay (MN assay) and the γ-H2AX assay are two assays used in radiobiology to study DNA DSB and repair. Breast cancer is the leading cancer amongst South African women, with a lifetime risk of 1 in 34. Since most cancer patients in South Africa present with late-stage disease, chemotherapy and radiotherapy are commonly-used treatments. Several international studies have shown breast cancer patients to be more chromosomally radiosensitive than healthy controls. These studies have not been confirmed on a cancer population living in South Africa. Cervical cancer is the second most common cancer in South Africa; however, it is the leading cancer amongst black women with a lifetime risk of 1/35 compared to 1/82 in white women. Studies show a genetic link to cervical cancer susceptibility and DNA damage repair genes. International studies on radiation-induced DNA damage in lymphocytes of cervical cancer patients remain inconclusive and have never been performed on a South African population. Cervical cancer is caused by infection with the Human Papilloma Virus (HPV). Human Immunodeficiency Virus (HIV), HPV and cervical cancer are epidemiologically linked. Due to the high rate of HIV in South Africa, a significant proportion of cervical cancer patients receiving radiotherapy treatment will be HIV-positive. Studies show an effect of HIV on chromosomal radiosensitivity, however this has not been confirmed on a cancer population. The MN assay on the biopsies and exfoliated cervical cells of cervical cancerItem Molecular characterisation of the Her2-Top2A amplicon in breast cancer(2010-09-17) Herd, Olivia JayneThe HER2 gene is amplified in 20-30% of breast cancers, a common cancer amongst South African women. HER2 amplification is associated with a poor prognosis and predicts response to treatments such as Herceptin. The gold standard for HER2 testing is Fluorescent in situ Hybridisation (FISH) with dual colour probes for the HER2 gene and chromosome 17 centromere (CEP17) internal control. According to international guidelines, a HER2/CEP17 ratio >2.2 is considered positive. The HER2 FISH test is complicated by the emergence of ambiguous cases with increased CEP17 signals that cannot be accounted for by chromosome 17 polysomy (> 6 copies of CEP17) and that may hide true HER2 gene amplification. The aims of this study were to characterise the HER2 amplicon, in particular the copy number of genes in the vicinity of the HER2 gene, and to design an alternative control probe that could clarify the HER2 gene status in ambiguous cases. In addition, results on 1558 breast cancer specimens sent for routine testing were analysed to determine the trends of HER2 amplification amongst South African women. The rate of HER2 gene amplification was significantly higher (p < 0.05) in African patients (52%) than in Caucasian patients (43%). In Caucasian women, the rate of HER2 amplification in the younger group (68%) was significantly higher (p < 0.05) than in the general Caucasian group (43%), while the same was not seen in the African cohort. Nineteen ambiguous cases with more than 9 copies of CEP17 were further investigated. FISH assays with four different probe kits (PathVysion HER-2: Poseidon Repeat free TOP2A, HER2, CEP17: and Vysis PML-RARA respectively) were performed to determine the copy number of the HER2, TOP2A, RARA genes and CEP17. An in-house dual colour probe kit was designed using the ACTG1 gene as a control for HER2. Of the 19 ambiguous cases, 16 had centromeric amplification, showing that CEP17 is no longer an adequate internal control in FISH HER2 testing. The TOP2A gene was only amplified in HER2 positive cases and the RARA gene was only amplified when the TOP2A gene was also amplified. FISH with ACTG1 as v a control clearly revealed HER2 amplification in ambiguous cases on image analysis and gave HER2/ACTG1 ratios significantly higher than HER2/CEP17 ratios. However, screening of an additional 40 unambiguous cases showed an increased copy number, although limited ( 8), of the ACTG1 gene in four patients; this warrants further testing to assess the value of this gene as a control. Interestingly, a trend was observed for ACTG1 increased copy number in HER2 negative cases, this may point to the presence of a driver gene whose amplification tends to be mutually exclusive from HER2 amplification.