Research shows small increase in risk until about five years after contraception is stopped, despite hopes that newer types might prove safer

All forms of the pill and other hormonal contraception carry a small risk of breast cancer, which lasts for about five years after women stop taking it, according to new research.

The increased risk has been known for some time, but there were hopes that newer forms of hormonal contraception – such as those which release progesterone only – would be safer. However, the new study in the New England Journal of Medicine confirms the 20% added risk that women run – although that is still very small for those not at high risk already.

Among women taking the pill for five years, the study suggests, there would be an extra one case for every 1500 women.

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The study is very large, including 1.8 million women in Denmark who were followed up for nearly 11 years on average. The Danish researchers found that the risk of breast cancer was higher in women who used the pill or other forms of hormonal contraception, including IUDs, for longer. It was also higher in those who were older – most of the breast cancer cases were in women over 40.

In a commentary with the study, Professor David Hunter, of the Nuffield Department of Population Health, said that the small risks of the pill needed to be set against the benefits, which included not only preventing an unwanted pregnancy but also a “substantial reductions in the risks of ovarian, endometrial and colorectal cancers in later life”.

But he called for more effort to be invested in safer forms of the pill. “These data suggest that the search for an oral contraceptive that does not elevate the risk of breast cancer needs to continue. In the 1980s and 1990s, there was some optimism regarding the development of a formulation that would reduce a woman’s risk of breast cancer, but research into this possibility appears to have stalled,” he writes.

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Kevin McConway, emeritus professor of applied statistics at the Open University, said the study found the increase in risk disappeared gradually over a few years once women stop taking the pill.



“Like most other studies on hormonal contraceptives and breast cancer risk, this one is observational, so it cannot prove conclusively that the hormonal contraception is definitely the cause of the increased risk. However, the researchers did allow statistically for most of the important factors that might also be involved, and they give good reasons why the differences in risk that they found are likely to be causally related to the contraceptives.

“I’m not a medical doctor, but my assessment is that this new evidence doesn’t make an important change to what was previously known about hormonal contraceptives and breast cancer risk. It just brings it further up to date and adds some detail. Certainly I’d advise anyone who is concerned about risks to talk to their doctor before making any changes in their contraceptive use.”