A study conducted by a group at Oxford showed that 200,000 lives have been saved from endometrial cancer over a 9-year period. This group, known better as the Collaborative Group on Epidemiological Studies on Endometrial Cancer (Oxford), showed that “about 400 000 cases of endometrial cancer before the age of 75 years have been prevented over the past 50 years (1965–2014) by oral contraceptives.” Their conclusion, based on this study, is that use of oral contraceptives (birth control pills), confers long-term protection against edometrial cancer.
To conduct this study, individual participant datasets were collected from 36 epidemiological studies. In these studies were 27,276 women with endometrial cancer (cases) and 115,743 without endometrial cancer (controls). As stated in the Methods in Supplementary Material for this study, “The relative risks (RRs) of endometrial cancer associated with oral contraceptive use were estimated using logistic regression, stratified by study, age, parity, body-mass index, smoking, and use of menopausal hormone therapy.”
Background on this study states that oral contraceptives are known to reduce incidence rate of endometrial cancer. This study set out to further understand how long this effect lasts after birth control pills are no longer taken, or whether this effect is modified by other factors. What the found is that the reduction in risk of endometrial cancer lasted for more than 30 years after oral contraceptive use ceased entirely.
No decrease between relative risks for use were shown during the 1960s, 70s, or 80s, “despite higher oestrogen doses in pills used in the early years.” This came after using birth control pills for periods of several years showed increased reduction of risk for endometrial cancer in this study. “The longer that women had used oral contraceptives, the greater the reduction in risk of endometrial cancer.”
The study went on to note that, in high-income countries specifically, “10 years use of oral contraceptives was estimated to reduce the absolute risk of endometrial cancer arising before age 75 years from 2·3 to 1·3 per 100 women.” Relative Risks of endometrial cancer associated with oral contraceptive use shown in this study were estimated using logic regression, stratified by study, age, parity, body-mass index, smoking, and use of menopausal hormone therapy.
For more information on this study, see the paper “Endometrial cancer and oral contraceptives: an individual participant meta-analysis of 27 276 women with endometrial cancer from 36 epidemiological studies.” This paper is published by the scientific publication The Lancet in Oncology in Volume 16, No. 9, p1061–1070. DOI: DOI: http://dx.doi.org/10.1016/S1470-2045(15)00212-0