Use of progestogen-only hormonal contraceptives is associated with a 20 to 30 percent higher risk of breast cancer, warned a study.

Breast cancer is one of the most common types of cancer worldwide, with around 2.3 million women diagnosed with the disease every year, according to the World Health Organization (WHO).

Until now studies have shown that the use of the combined contraceptive pill, which combines estrogen and progestogen, is associated with a small increase in the risk of developing breast cancer, and that declines after stopping use.

For the study, researchers at Oxford Population Health’s Cancer Epidemiology Unit analyzed data from 9,498 women who developed invasive breast cancer between the ages of 20 to 49. They closely matched it with 18,171 women without breast cancer who acted as controls.

The results, published in the journal PLOS Medicine, showed a significant increase in the risk of breast cancer associated with hormonal contraceptive use, regardless of whether the contraceptive last prescribed was a combined (estrogen and progestogen) oral preparation (23 percent), a progestogen-only oral preparation (26 percent), an injected progestogen (25 percent), or a progestogen-releasing intra-uterine device (32 percent).

Further, the increased risk of breast cancer associated with oral contraceptive use declined after stopping use.

The increased risks were: last prescribed within the last year (33 percent); last prescribed one-four years ago (17 percent); last prescribed five or more years ago (15 percent).

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“The new findings suggest that current or recent use of all types of progestogen-only contraceptives is associated with a slight increase in breast cancer risk, similar to that associated with the use of combined oral contraceptives,” said Kirstin Pirie, statistical programmer at Oxford Population Health.

“Given that a person’s underlying risk of developing breast cancer increases with advancing age, the absolute excess risk of breast cancer associated with either type of oral contraceptive will be smaller in women who use it at younger ages. These excess risks must, however, be viewed in the context of the well-established benefits of contraceptive use in women’s reproductive years,” Pirie said.

When the findings for progestogen-only contraceptives were combined with previously published studies, there was an increased risk of breast cancer in current and recent users of all four types of progestogen-only preparations: oral (29 percent), injected (18 percent), implanted (28 percent), and intrauterine devices (21 percent).

The researchers estimated that the absolute excess risk of developing breast cancer over a 15-year period in women with five years of use of oral contraceptives ranged from eight in 100,000 women for use from age 16 to 20, to 265 in 100,000 for use from age 35 to 39.

“For anyone looking to lower their cancer risk, not smoking, eating a healthy balanced diet, drinking less alcohol, and keeping a healthy weight will have the most impact. There are lots of possible benefits to using contraception, as well as other risks not related to cancer. That’s why deciding to take them is a personal choice and should be done after speaking to your doctor so you can make a decision that is right for you,” said Claire Knight, Senior Health Information Manager at Cancer Research UK.