Association of intimate partner vasectomy, use of long-acting progestogen-based contraceptives and intra-uterine contraceptive devices with risk of ovarian cancer.
Thesis DisciplineHealth Sciences
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Background: Ovarian cancer is an aggressive and fatal disease affecting women worldwide. Though the pathogenesis and causes of ovarian cancer have not been established, some risk factors are well known. Use of oral contraceptives and tubal ligation have been shown to be inversely associated with ovarian cancer. What has not been clearly demonstrated is the association between intimate partner vasectomy, use of intrauterine contraceptive devices, and long-acting progestogen-based contraceptives and the risk of ovarian cancer. The limited scope for early detection of this neoplasm, and poor survival despite advances in treatment, make prevention especially important. Objectives: This study sought to investigate whether there were associations between the use of long-acting progestogen-based contraceptives, intrauterine contraceptive devices (IUDs), and vasectomy of a woman’s sexual partner, and ovarian cancer. Methods: This was a New Zealand nationwide population-based case-control study involving women aged 35-69 years. Controls were randomly selected from the New Zealand electoral roll. Cases were women with a diagnosis of incident ovarian cancer recruited from the New Zealand Cancer Registry (NZCR) and had to be listed on the electoral roll. A postal questionnaire was used to gather information on socio-demographic characteristics, contraceptive use, and risk factors for ovarian cancer. Data were analysed using IBM Statistical Package for the Social Sciences (IBM SPSS statistics 22). Age-adjusted analyses were done using the method of Mantel and Haenszel. In multivariate analyses, binary logistic regression was used. Approval to conduct the study was obtained from the Southern Health and Disability Ethics Committee (13/STH/26) and the University of Canterbury Human Ethics Committee (HEC 2013/08). Results: Between 1st May 2013 and 31st October, 2015, 1,903 controls were approached. Of these 1,735 were eligible for the study and 837 participated in the study (response proportion of 48.2%). Of the 837 participants, after reviewing the questionnaires, 91 were excluded because they had prior history of bilateral oophorectomy or ovarian cancer, or were more than 69 years of age. In the same period, 258 cases were received from NZCR out of whom 205 were eligible and 152 took part (response proportion of 74.1%). Ever-use of vasectomy was inversely associated with ovarian cancer (OR = 0.67; 95% CI = 0.46-0.96). Each year of use was associated with an OR of 0.97 (95% CI = 0.94-1.00). Ever-use of DMPA was associated with an OR of 0.70 (95% CI = 0.38-1.30). Age at first use, duration of use, and time since last use of DMPA were not statistically significantly associated with ovarian cancer. Although ever-use of IUDs was not associated with ovarian cancer (OR = 0.98; 95% CI = 0.66-1.47), longer duration of use was associated with higher risk (P-trend = 0.030) and longer time since last use was inversely associated with ovarian cancer (P-trend = 0.032). There were also statistically significant inverse associations between ovarian cancer and use of oral contraceptives, parity, and breastfeeding. Conclusion: The findings of this study suggest that ovarian cancer may be inversely associated with use of DMPA and partner vasectomy and positively associated with use of intrauterine contraceptive devices. However, these findings are not definitive; a study with greater power, or a collaborative analysis of existing studies, is needed to better assess these associations.