Oral contraceptives have prevented approximately half a million cases of endometrial cancer in industrialized nations over the past 50 years. This is the conclusion of a large-scale meta-analysis of 36 epidemiological studies.
The data set of the UK case-control study consisted of a total of 27,276 women with and 115,743 women without endometrial cancer. The median age was 63 years. The median duration of oral contraceptive use was three years in the case sample and 4.4 years in the control sample. Overall, 35% of the former group had ever taken the pill (“ever-users”), and 39% in the latter group. Geographic regions represented in the studies included Europe, Asia, Australia, North America and South Africa.
Longer intake – greater risk reduction
The question of the effect of oral contraceptives on the incidence of endometrial cancer is not new. A protective relationship has already been shown in previous studies. It is not yet fully understood how long the protective effect lasts after discontinuation of the pill and what other factors influence the association. The following findings emerge from the current study:
- The longer a woman takes oral contraceptives, the lower her risk for endometrial cancer. Each five-year extension of intake significantly reduced the hazard by 24% (RR 0.76; 95% CI 0.73-0.78; p<0.0001).
- In high-income industrialized nations, the researchers calculated an absolute risk reduction from 2.3 to 1.3 per 100 women before age 75 after 10 years of contraceptive use. While 23 out of 1,000 women who did not take the pill at all fell ill, 13 out of 1,000 women who took the pill for more than ten years suffered the same fate.
- The magnitude of risk reduction from taking oral contraceptives depends on several factors. The type of tumor plays an important role: carcinomas are prevented to a greater extent than sarcomas. The associated risk ratios were 0.69 (95% CI 0.66-0.71) and 0.83 (0.67-1.04). This difference within the case group was significant (p=0.02).
- In contrast, the estrogen dose, which was still significantly higher especially in the early years of the introduction of the pill, had no influence. Today’s pills, which contain much less estrogen, protect equally well as the older generation pills.
- The risk reduction persisted for more than 30 years after discontinuation of the pill. Women who took the pill in their twenties still benefited from the protection mentioned above when they were over 50.
Numerous cases of illness prevented
The authors conclude that the pill has prevented about 400,000 cases of endometrial cancer before age 75 in the last 50 years since 1965, 200,000 of them in the last decade alone.
Source: Collaborative Group on Epidemiological Studies on Endometrial Cancer: Endometrial cancer and oral contraceptives: an individual participant meta-analysis of 27 276 women with endometrial cancer from 36 epidemiological studies. The Lancet Oncology 2015.
InFo ONCOLOGY & HEMATOLOGY 2016; 4(1): 6.
