Oral contraceptives offer long-term protection against endometrial cancer,
according to new research published in the Lancet Oncology (dx.doi.org/10.1016/ S1470-2045(15)00212-0).

Researchers combined individual data from 27,276 women with endometrial cancer and 115,743 controls who took part in one of 36 epidemiological studies. Endometrial cancer was diagnosed at a median age of 63 years. Thirty-five per cent of women with endometrial cancer and 39% of controls had used oral contraceptives, for medians of 3.0 and 4.4 years respectively.

Overall, the Pill reduced endometrial cancer risk by 31%. The longer women took the Pill, the greater the reduction: each 5 years of oral contraceptive use was associated with a 24% reduction in the risk of endometrial cancer. Women who used oral contraceptives for between 10 and 15 years (median 11.8 years) were 48% less likely to develop endometrial cancer than those who never took the Pill.

The reduced risk “persisted for more than 30 years” after women stopped taking oral contraceptives and did not seem to differ between those who took the Pill during the 1960s, 1970s and 1980s, despite higher oestrogen levels in the earlier contraceptives. The Pill’s protective effect did “not seem to depend much” on characteristics such as parity, adiposity or menopausal status. However, oral contraceptives seemed to show greater protection against carcinomas (31% reduction) than sarcomas (17% reduction). 

In high-income countries, the authors estimate, oral contraceptives reduced the absolute risk of endometrial cancer before 75 years of age from 2.3 per 100 women among never-users to 1.7, 1.3 and 1.0 per 100 women who took the Pill for 5, 10 and 15 years respectively. The authors estimated that in developed countries, oral contraceptives prevented about 400,000 endometrial cancers in women aged 30 to 74 years between 1965 and 2014, including 200,000 cases between 2005 and 2014.