Family history of cancers, hormone replacement therapy and the risk of breast cancer in Canada
By: by Margarita Parthimos.
Published: 2006
Language: eng
Number of pages: 146
ISBN-13: 9780494159125
Description: Recent evidence of the effect of hormone replacement therapy (HRT) revealed an increased risk of postmenopausal breast cancer associated with the estrogen-progestin combination pill, though a decreased risk for exposure to estrogen alone. At the time of planning of this study, there was much inconsistency in findings from observational studies, explained, in part, by the differing estrogenic potencies over time, the introduction of progestin to estrogen therapies, and the examination of different time windows of exposure between studies. The impact of HRT may also differ by the family history of cancer, though this relationship has not been thoroughly studied. The objectives of this study were to determine whether a family history of different cancers, as measured by a family history score (FHS), and ever use of HRT use were associated with the risk for postmenopausal breast cancer, and whether there was evidence of an FHS-HRT interaction.Results indicate that HRT users were not at increased risk of postmenopausal breast cancer (OR=0.74, 95%CI: 0.52-1.05) compared to non-users. Relative to no family history of these cancers, women with a family history of cancer of the breast (OR=2.45, 95%CI: 1.37-4.36) and breast or ovary (OR=2.28, 95%CI: 1.35-3.85) were at increased risk of postmenopausal breast cancer. The FHS-HRT interaction was not statistically significant, however, analyses stratified by category of FHS (high, low, none) revealed a significant inverse effect of HRT use in women at highest risk for both a family history of cancer of the breast (OR=0.27, 95%CI: 0.10-0.71), and breast or ovary (OR=0.22, 95%CI: 0.09-0.53). These significant inverse associations are suggestive of a beneficial effect of HRT for women at highest risk based on their family history, and suggest estrogen as a viable alternative to prophylactic mastectomy and oophorectomy, as approximately 85% of HRT users reported exposure to estrogen alone. This requires further study.A case-control study nested within the Canadian National Breast Screening Study was conducted, with controls selected via incidence-density sampling at a case:control ratio of 4:1. Study participants (n=1,255) were stratified by menopausal status with only postmenopausal women (n=671 cases, 216 controls) included in the HRT and FHS-HRT interaction analyses.
Notes: Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3739.

Thesis (Ph.D.)--University of Toronto, 2006.

Includes bibliographic references.

Electronic version licensed for access by U. of T. users.