Oral contraceptive use lowers endometrial cancer risk

by Bruce Sylvester: Oral contraceptive use appears to provide long-term protection against endometrial cancer, researchers reported on August 4, 2015 in The Lancet Oncology.

Investigator Dr Naomi Allen, of the University of Oxford, UK, said about the findings, “The existing evidence suggests that medium-to-long-term use of oral contraceptives [5 years or longer] results in substantially reduced risk of endometrial cancer. Over the past 50 years [1965-2014], we estimate that about 400,000 endometrial cancers have been prevented in women before the age of 75 years in high-income countries through the use of oral contraceptives, with about 200,000 prevented during the last decade [2005-14].”

Co-investigator Professor Valerie Beral, also from the University of Oxford in the UK, added. “The strong protective effect of oral contraceptives against endometrial cancer — which persists for decades after stopping the pill — means that women who use it when they are in their 20s or even younger continue to benefit into their 50s and older, when cancer becomes more common.”

The investigators pooled and analyzed data from 36 endometrial cancer  studies in North America, Europe, Asia, Australia, and South Africa. The studies included 27,276 subjects and over 100,000 controls.

They found that every 5 years of oral contraceptive use reduced endometrial cancer risk by about 24 per cent, and  10 years reduced the risk of endometrial cancer before age 75 from 2.3 to 1.3 cases per 100 subjects.

Reductions in endometrial cancer risk persisted for at least 30 years after termination of oral contraceptive use. And the finding held for boith the high-dose oral contraceptives used in the 1960s and lower-dose oral contraceptives used more recently.

The researchers reported that 10-15 years of oral contraceptive use correlated to an approximately 50 per cent reduction in the risk of endometrial cancer.

They noted that proportional risk reduction for endometrial cancer did not vary significantly with reproductive history, adiposity, alcohol use, tobacco use, or ethnicity.

This study was funded by the Medical Research Council and Cancer Research UK.