Menstrual cycle can affect breast cancer screening

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The Independent Online
Women are twice as likely to wrongly be given the all-clear during breast cancer screening if they go for the test during the last two weeks of their menstrual cycle, researchers warn today.

A study of 8,887 menstruating women found that when breast cancer screening was carried out during the last 14 days of their menstrual cycle, they faced double the risk of being told they had not got cancer when in fact they had, compared with those who had the test during the first two weeks.

Researchers claim their findings could explain why women under 50 do not benefit from mammogram screening as much as older women. The research, published today in the medical journal Cancer, examined data of menstruating women aged 40-44 collected by the Canadian National Breast Screening Study.

Researchers compared mammogram results of women during days one to 14 of their menstrual cycle with those in the last 14 days. They also looked at whether the women had taken hormones in the form of oral contraceptive or replacement therapy, and found most of them had or were continuing to use them.

The risk was found to be reduced among women who had never taken hormones.

Mammograms are well known in the medical world to be less accurate in younger women than older women.

Researchers claim this study shows there is an opportunity to improve the accuracy of mammograms by choosing to have the tests done during the first half of the menstrual cycle.