The Pill linked to increased breast cancer risk

A new statistical analysis finds that women under age 50 who were diagnosed with breast cancer were also more likely to have recently been on some versions of the Pill.

The increased cancer risk still translates to less than a 1% chance of developing breast cancer for most younger women, researchers emphasise, so the results should not outweigh the many benefits of taking oral contraceptives.

These results are not enough to change clinical practice or to discourage any women from taking birth control pills, said lead study author Elizabeth F Beaber of the Fred Hutchinson Cancer Research Center in Seattle, Washington.

Some past research suggests that the hormones in birth control pills could “feed” hormone-sensitive tumours and thereby raise younger women’s risk of a breast cancer diagnosis, or of developing more aggressive cancers.

However, birth control pills have evolved over the decades since their introduction and the hormone doses they contain have dropped steadily, so many studies are based on data for formulations that are no longer used, Beaber and her colleagues write in the journal Cancer Research.

To examine the risk in a group of women more recently taking birth control pills, Beaber’s team analysed data from a large healthcare delivery system, tracking birth control pill prescriptions and breast cancer diagnoses.

The researchers compared 1,102 women diagnosed with invasive breast cancer between 1990 and 2009 with 21,952 women without cancer who were of similar age.

Women who had taken oral contraception during the past year, according to pharmacy records, were more likely to be in the cancer group than those who had never taken birth control pills or who had taken them more than a year prior.

Contraceptives that contain higher doses of oestrogen or progestin were more strongly associated with increased cancer risk.

“Use of formulations with high dose oestrogen, ethynodiol diacetate [synthetic progestin], and specific triphasic oral contraceptives in the past year was associated with an increased breast cancer risk in our study, while other formulations, including low dose oestrogen oral contraceptives, did not appear to be associated with an elevated risk,” said Beaber.

Overall, the risk was higher for hormone-sensitive cancers than for other types of tumours, but that result was not statistically significant, meaning it could have been due to chance.