Abstract:
Human papillomaviruses (HPV) can cause benign or malignant disease with the majority of infections without symptoms. The viral origin of cervical cancer is now proven with HPV proteins E6 and E7 defining part of the molecular
basis of oncogenesis in vitro. Integration and/or malignant transformation of
cervical cells in vivo are expected to be accompanied by the over-expression of
HPV genes for E6 and E7 oncoproteins and a reduction of both expression for
the L1 capsid protein and viral DNA. Cervical intraepithelial neoplasia (CIN) has
been associated with particular HPV types that can be distinguished by DNA
sequence differences. The research work studied two important aspects of HPV
and its role in cervical disease. First, the distribution of HPV types and the
epidemiology of HPV infection in a population of Saskatchewan women referred
to a colposcopy clinic. Second, the potential of HPV-16 transcripts and HPV viral
load for the detection of CIN.
The most commonly identified genotype in patients with CIN grade 2 or
worse was HPV-16 (46.7%) followed by HPV-31 (14.7%) and then HPV-18
(3.9%). The risk of CIN associated with HPV-18 infection, odds ratio 0.8 (95%
CI, 0.4 to 1.7) is significantly lower than either the odds ratio of 6.3 for HPV-16
(95% CI, 3.6 to 11.0) or 4.3 for HPV-31 (95% CI, 1.8 to 12.6). Thus in
Saskatchewan, the prevalence of HPV-31 is high whereas HPV-18 is associated
with less clinical disease. Consequently, the efficacy the new cervical cancer
vaccine, which target only HPV-16 and HPV-18, may be diminished in
Saskatchewan’s population.
Analysis of variance (P = 0.2) indicated no significant correlation between
grade of CIN and HPV viral load. The presence of E6 RNA (P = 0.0002) and
relative quantification of HPV-16 E6 transcripts (P < 0.0001) displayed the most
significant median difference among the various grades of CIN when
standardized to HPV viral load and human RNA and DNA levels. There was no
correlation with L1 transcripts and cervical disease. Likelihood ratios indicate
that the combination of Pap smear cervical cytology screening test with E6
relative quantification, on populations with higher cervical disease prevalence,
would find more true positives than simply an additional Pap test. Using
molecular testing for triage, HPV genotype information identifies 96% of women
with CIN grade 2 or worse while eliminating 44% of women with CIN grade 1 or
better. Information from the relative quantification of HPV-16 E6 transcripts
identified 31.0% (n=13) of HPV-16 positive women with CIN grade 1 or better
while retaining 92.4% of women with CIN grade 2 or worse.
This work shows that there is diagnostic utility in relative quantification of
HPV transcripts and that it benefits from standardization for variables such as the
amount of HPV DNA and the total cellular nucleic acids. Relative quantification
of HPV-16 E6 and HPV genotyping can be used to reduce medical procedures
for women. HPV molecular tests could be useful in a cascade of diagnostic
testing designed to refer women with cervical abnormalities for colposcopy, or
treatment, while reducing the number of women needing triage.
Description:
A Thesis
Submitted to the Faculty of Graduate Studies and Research
In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy, University of Regina. xv, 170 l.
