Birth Control Pill Linked to Increased Glioma Risk

Hormonal contraceptive use is associated with an increased glioma risk

A history of hormonal contraceptive use in younger women for 5 years or more was found to be associated with a possible increased risk of glioma, a rare type of brain tumor. The findings of the study were published in the British Journal of Clinical Pharmacology.

Prior studies have shown that female sex hormones, the active ingredients of hormonal contraceptives, may increase the risk of some cancers while reducing the risk of other cancers. This was the starting point of the study for author David Gaist, MD, PhD, of the Odense University Hospital in Southern Denmark, and colleagues.

“It is important to keep this apparent increase in risk in context,” said Gaist in a statement. While the study did find a link, the benefit of hormonal contraceptives still outweighs the risk.

Exposure to a hormonal contraceptive was categorized based on the hormone type: estrogen-progesterone or progesterone only, and by duration of use (less than 1 year, 1 year to 5 years, and more than 5 years).

Ever use of hormonal contraceptives was associated with a 50% relative increased risk of glioma, while those who used contraceptives for more than 5 years had a 90% relative increased risk. The women who used progesterone-only contraceptives had a greater risk compared with those on an estrogen-progesterone contraceptive. Those who were current hormonal contraceptive users had a 70% relative increased risk of glioma compared with past users, who had a 20% relative increased risk.

Analyzing the results by histological types of glioma, there was a slightly higher risk of glioblastoma multiforme.

Gaist and colleagues used data from Denmark’s national administrative and health registries. The authors identified women between the ages of 15 and 49 and a diagnosis of glioma between 2000 and 2009. Each of the 317 cases of glioma were compared with 2,126 age-matched women with no glioma diagnosis-8 for every case.

Of the 317 cases, 114 occurred in women between the ages of 15 and 34, 115 occurred in women between the ages of 35 and 44, and 88 occurred in women between 45 and 49 years of age.

Previous case-control and cohort studies either found no association, a weak inverse association, or an increased risk between glioma incidence and hormonal contraceptive use, but several of these studies only analyzed former hormone contraceptive users over the age of 50.

“In a population of women in the reproductive age, including those who use hormonal contraceptives, you would anticipate seeing 5 in 100,000 people develop a glioma annually, according to the nationwide Danish Cancer Registry,” said Gaist.

According to Gaist, tracking women who use contraceptives long term is needed to further assess the risk. The authors noted that there may be confounding factors such as the tendency of women who take contraceptives to get more regular checkups. Still, “considering the extensive use of hormonal contraceptives our finding merits further investigation,” stated the authors.