In this thesis we examine the effect of hormone replacement therapy (HRT) on the risk of colorectal cancer. Also examined are the effects of oral versus transdermal estrogen replacement therapy, methods of defining estrogen exposure, selection bias, and trends in the use of HRT over the last two decades. / A nested case-control study was conducted using records from Saskatchewan Health's administrative databases. Information on covariates not available from the databases was collected during interviews, from a subgroup of subjects. Incidence density sampling was used to age match controls (four per case, N = 12,116) to each of 3,059 cases accrued in the province from 1981 to 1998. / Short and long durations of HRT use (<5 years and ≥5 years) were associated with odds ratios (OR) of 0.86 (0.76--0.97) and 0.78 (95% CI: 0.64--0.86), respectively. Stratification according to history of having had a screening sigmoidoscopy did not eliminate the observed protective effect. Important differences were not seen between more recent HRT use (<5 and <10 years), compared with more distant past use (≥5 and ≥10 years). / The use of various definitions of estrogen exposure produced ORs ranging from 0.78 to 0.99 which are similar to results from almost two dozen observational studies conducted over the past two decades indicating that this is an important source of variability that needs to be considered. / The study of independent effects of oral and transdermal estrogens revealed a protective effect of transdermal estrogen that was much greater than that of oral estrogen and which has not previously been reported. A protective effect remained when women who had used oral estrogen only were used as the reference group. / Data pertaining to lifestyle factors collected by interview appeared not to alter ORs for HRT and colorectal cancer. However, due to extremely low response rates in the interview phase of the study, 30% among cases and 18% among controls, we were unable to conclude whether or not confounding was eliminated. / An important finding of research is the strong observed protective effect of transdermal estrogen replacement therapy. This demonstrates the importance of taking into consideration the mode of estrogen delivery in studies where the associations between HRT use and health outcomes are examined.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.38476 |
| Date | January 2002 |
| Creators | Csizmadi, Ilona |
| Contributors | Collet, Jean-Paul (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Epidemiology and Biostatistics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001941109, proquestno: NQ85698, Theses scanned by UMI/ProQuest. |
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