In an individual-patient meta-analysis reported in The Lancet Oncology, the Collaborative Group on Epidemiological Studies on Endometrial Cancer found that oral contraceptive use was associated with long-term protection from endometrial cancer. Reduction in risk was greater for carcinomas than sarcomas.
The study included data from 27,276 women with endometrial cancer (cases) and 115,743 controls without endometrial cancer from 36 epidemiologic studies. The relative risks 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.
Cases had a median age of 63 years, and the median year of cancer diagnosis was 2001. Overall, 9,459 (35%) cases and 45,625 (39%) controls had ever used oral contraceptives, with a median duration of use of 3.0 years and 4.4 years.
Increased duration of oral contraceptive use was associated with a greater reduction in the risk of cancer, with every 5 years of use being associated with a relative risk of 0.76 (P < .0001). Reduction in risk persisted for > 30 years after oral contraceptive use had stopped; there was no apparent decrease in the relative risks associated with contraceptive use during the 1960s, 1970s, and 1980s, despite the higher estrogen doses used in earlier periods.
The reduction in risk with ever use of oral contraceptives was greater for carcinomas (relative risk = 0.69, 95% confidence interval [CI] = 0.66–0.71) than for sarcomas (relative risk = 0.83, 95% CI = 0.67–1.04; P = .02 for case-case comparison).
In resource-rich countries, 10 years of oral contraceptive use was estimated to reduce the absolute risk of endometrial cancer before age 75 years from 2.3 to 1.3 per 100 women.
The investigators concluded: “Use of oral contraceptives confers long-term protection against endometrial cancer. These results suggest that, in developed countries, 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, including 200,000 in the past decade (2005–2014).”
The study was funded by the Medical Research Council, Cancer Research UK.
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