Birth control pill use for 15 years may cut lifetime risk of endometrial cancer in half

The birth control pill gives women long-term protection against endometrial or womb cancer, according to a large new review.

Oral contraceptives, or the pill, have been approved for birth control since the 1960s. Since then, balancing the risks and benefits has been complex.

U.K. researchers have grouped together data from 27,276 women with endometrial cancer in 36 studies from North America, Europe, Asia, Australia, and South Africa to examine the effects of oral contraceptives on cancer risk.

About 10 to 15 years of use of the pill halves the lifetime risk of endometrial cancer, study author Prof. Valerie Beral from the University of Oxford in the U.K. and her co-authors said in Tuesday's online issue of the Lancet Oncology journal.

"Women who are alive now in the West, a large proportion have taken the pill," Beral said in an interview. "We've got very reliable data. As far as cancer is concerned, they're better off if they've taken the pill."

In high-income countries, use of the pill for 10 years reduces the risk of developing endometrial cancer before age 75 from 2.3 to 1.3 cases per 100 users, the researchers estimated.

The estrogen dose in birth control pills is now about a quarter of what it was originally, Beral said. But the amount of hormones in the lower-dose pills is still enough to reduce the risk of endometrial cancer, the researchers said.

They further estimate about 200,000 cases of endometrial cancer before age 75 have been prevented in the past decade in developed countries.

Part of the complexity of assessing the pill is its varied side-effects in the short and long term, Nicolas Wentzensen and Amy Berrington de Gonzalez of the U.S. National Cancer Institute in Bethseda, Md., said in a journal commentary.

Use of the pill is associated with benefits including the prevention of ovarian cysts, fibroids and acne.

The risks include:

• Venous thrombosis or clots.
• Stroke in young women.
• Heart attacks.
• Cervical cancer.
• Breast cancer.

As soon as women stop taking the pill, the risk of thrombosis and stroke go away, Beral said. 

The estrogen dose and formulation of birth control do seem to matter for harmful cardiovascular outcomes such as clots, heart attacks and strokes, the commentators said.

"Women need to be more aware of the unintended benefits and the risks of oral contraceptives so that they can make informed decisions," Wentzensen and de Gonzalez concluded.

Dr. Ida Ackerman is a radiation oncologist at Sunnybrook Health Sciences Centre in Toronto who studies and treats gynecological cancers.

"[The pill] is more safe than it used to be," Ackerman said. "But I'm not sure the magnitude of the benefit is great enough to warrant recommending it routinely, especially I think when one recognizes that the majority of endometrial cancers present early and the majority are cured."

The study was funded by the Medical Research Council and Cancer Research U.K.