Content area
Full Text
Key words: combined oral contraceptives, endometrial neoplasms, Sweden.
Abstract
Objectives: To estimate the magnitude and persistence of the protective effect of use of combined oral contraceptives (COCs) and endometrial cancer risk.
Methods: We performed a nation-wide, population-based case+ or -control study among postmenopausal women aged 50+ or -74 years in Sweden, which included 709 subjects with incident, histopathologically verified endometrial cancer, and 3,368 controls with an intact uterus. We used unconditional logistic regression to calculate odds ratios as estimates of relative risks.
Results: Use of any sort of oral contraceptive decreased risk for endometrial cancer by 30%, while progestin-only pills reduced risk more markedly. For COCs the reduction in risk was noticeable following 3 or more years of use (OR 0.5, 95% CI 0.3+ or -0.7), and increased with duration of intake, reaching 80% lower risk after 10 years of use. The protective effect of COC use was similar for all degrees of tumor differentiation and invasiveness, and remained for at least 20 years after cessation of use. Subsequent use of hormone replacement did not modify these protective effects.
Conclusions: We conclude that COC use confers a long-lasting protection against endometrial cancer risk which is particularly marked for long-term users.
Introduction
Use of combined oral contraceptives (COCs), i.e. formulations with synthetic high-potency estrogens and progestins, has consistently been found to markedly reduce the risk for endometrial cancer [1]. However, several aspects of this association remain to be clarified, including effects after long-term use, persistence of the protective association, effects on aggressive versus minimally invasive tumors, and the impact of subsequent use of hormone replacement. We report here findings from a large, population-based case-control study in Sweden with detailed assessment of exposure and a uniform histopathological review of all cancers.
Materials and methods
Subjects
This population-based case+ or -control study was conducted among women aged 50+ or -74 years, born in Sweden and resident there between 1 January 1994 and 31 December 1995. We restricted our study to postmenopausal women with an intact uterus and no previous endometrial or breast cancer diagnosis. Eligible cases (n = 1055) were women with an incident, newly diagnosed, histopathologically confirmed endometrial cancer. They were identified through the six regional cancer registries in Sweden, which provide a virtually complete cancer...