Mammograms are effective at detecting early-stage breast cancer in women who've had the disease, but are less accurate in this group than in those without a history of the disease, according to a new study.

Compared to women without a history of breast cancer , those with a history had more false positives, meaning mammograms identified more possible trouble spots that later turned out not to be cancer.

Women with a history of breast cancer also had more interval cancers, which are cancers that show up in between mammograms . Interval cancers are found when a woman develops symptoms that bring her to her doctor's office.

The results support the current recommendation that women with a history of breast cancer get mammograms every year, the researchers said. However, some of these women, such as those under age 50 and those with very dense breast tissue , might benefit from the use of alternative screening tools, such as a breast ultrasound or MRI, said study researcher Diana Miglioretti, a senior investigator at Group Health Research Institute in Seattle. But further research is needed to determine whether such screening would be beneficial, she said.

The study will be published tomorrow (Feb. 23) in the Journal of the American Medical Association.

Mammogram screening

Women who've had breast cancer face an increased risk of developing the disease again, compared with women who've never had it. While they usually receive mammograms every year, there is little evidence to show this practice is really effective, the researchers said.

Miglioretti and her colleagues analyzed information from 19,078 women with a history of breast cancer who received 58,870 mammograms over a 12-year period. They also looked at data from 55,315 women without a history of breast cancer who received 58,870 mammograms. Both groups were similar in breast density, age and the year of their mammogram.

Women with a history of breast cancer had about twice the risk of developing the disease again over the study period, compared with those without a history of breast cancer the researchers found 655 cancers in women with a history, but 342 cancers in women without a history.

The mammogram test was 65.4 percent sensitive for those with a history of breast cancer, meaning the screening identified breast cancer 65.4 percent of the time when cancer was present. For those without a history of breast cancer, the test's sensitivity was 76.5 percent.

About 1.7 percent of women with a history of breast cancer had a false-positive result, whereas only about 1 percent of women without a history of breast cancer had false positives, Miglioretti said.

Will more frequent mammograms help?

The researchers don't know whether mammograms were less sensitive for women with a history of breast cancer because the mammograms just weren't detecting their cancers, or because cancers in these women grow more rapidly, and tend to show up in between screenings.

If the former is the case, having more frequent mammograms wouldn't help, Miglioretti said.

For now, these women are recommended to have yearly mammograms, but there are a few cautions to consider, she said.

"These women are at higher risk of having an interval cancer, so they need to be vigilant, and if they have any breast concerns, seek a doctor," Miglioretti said. And these women should be aware that there's a high likelihood they are going to need additional imaging or biopsies, Miglioretti said.

Pass it on: Mammograms are less accurate for women with a history of breast cancer than they are for women without a history of breast cancer.

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