Mammograms and the Menstrual Cycle
HealthNews from the publishers of the New
England Journal of Medicine
Experts have long advised women to do breast self-exams right after
their menstrual periods. Now, new evidence suggests this is also the best
time to have a mammogram. According to a report in the August 15
Cancer, mammograms done during the first two weeks of a woman's
menstrual cycle are less likely to miss breast tumors than those done
during the second two weeks of the cycle.
Researchers studied 8,887 women ages 40 to 44 who had yearly mammograms
and manual breast exams as part of the Canadian National Breast Screening
Study. They compared mammogram results of women tested during the first
half of their menstrual cycle (day 1 to 14) with those tested during the
second half (day 15 to 28).
The most striking findings were among women who had previously taken or
were currently on oral contraceptives or hormone replacement therapy,
which included about 75 percent of the women in this study. Women tested
toward the end of their cycles had twice as many false negative results,
meaning the mammogram was deemed nonsuspicious, even though cancer was
actually present. If mammography fails to detect a tumor, the cancer
sometimes is picked up by breast self-exam or if a doctor or nurse does a
breast exam at the same time, as occurred in this study. But sometimes all
these methods miss the cancer. False negatives during the second half of
the cycle were slightly less common in women who had never taken hormones.
Breast tissue tends to be denser during the second half of the
menstrual cycle, so it makes sense that mammograms done during that time
would be harder to read, notes HealthNews associate editor Carolyn Runowicz,
MD. "Every premenopausal woman over 40, regardless of her hormone use,
should schedule her yearly mammogram in the week after her period ends and
have her health care provider do a breast exam at the same time," she
says.
