Women who are told that their suspicious mammogram was a false alarm are more likely to delay their next scheduled mammogram, or possibly not show up for their next screening at all.
The finding, in a study of 261,767 Chicago-area women in the journal Cancer Epidemiology, Biomarkers and Prevention, highlights an unintended consequence of such false alarms, known as false positives.
In cases where a mammogram was recommended every year, women who had an unfounded scare tended to delay their next test by an additional 13 months compared to a three- to six-month delay for women whose tests had come out negative.
That, in turn, can affect a woman's chances of survival if breast cancer is subsequently diagnosed.
Among women who had not experienced a false alarm, their odds of being diagnosed with an advanced tumor were 0.3 percent. The odds for a woman who had experienced a false alarm were slightly but significantly higher at 0.4 percent.
Some women never showed up at all, but the researchers couldn't determine whether they gave up on the breast cancer screening or simply had it done elsewhere.
"It's a delicate balance," chief author Firas Dabbous of Advocate Lutheran General Hospital in Park Ridge, Illinois, told Reuters Health. "We want to detect tumors when they are present but we don't want to overburden women with a lot of false positives and a workup that is not needed."
Debates over how often women should get mammograms often focus on whether false positives - which can cause women to experience anxiety as well as painful and expensive extra testing, including biopsies – represent a harm that outweighs the benefits of screening.
"The delays the authors observed were significant," Robert Smith, vice president for cancer screening at the American Cancer Society, told Reuters Health by email. "If these findings can be validated in other studies, then it suggests that extra attention should be dedicated to insuring that women with false positive findings are reminded to return to annual or biennial screening with sufficient notice and multiple reminders."
Being told that a breast X-ray has uncovered something suspicious is always stressful, even though most women are also told that, in the vast majority of cases, there is no problem.
Women who have a mammogram have a chance as high as 1 in 10 of getting a false positive. In fact, a woman who has an annual mammogram has a 50-50 chance of having one false positive every decade. An estimated 7 percent to 17 percent of those will require a biopsy.
Previous studies that have tried to assess how false positives affect the willingness to have a future mammogram have produced mixed results.
"Most U.S. studies have shown either greater adherence to screening recommendations after a false positive, or no difference, whereas studies done in Europe have shown screening rates somewhat lower than women who have true negative results," Smith said.
The Dabbous team looked at 741,150 screening mammograms done at a large healthcare organization.
In 12.3 percent of the cases, there was something suspicious but it turned out to be a false alarm.
During the three years after that initial mammogram, 77.9 percent of the women with a false positive result had a subsequent mammogram compared to 85.0 percent of the women who had not experienced a false alarm.
Biopsies seemed to play a significant role in whether a woman came back for another mammogram. Compared to patients who had received a false positive and simply received additional imaging, women who also got a biopsy were 19 percent less likely to come back for a regular mammogram.
It’s not known if the false positive experience prompted some women to give up on mammograms, said Dabbous, who is manager of patient centered outcomes research at Advocate's Russell Institute for Research and Innovation.
The lesson for women remains "to encourage women to adhere to mammography screening and come back on time because this is the only tool that we have that is literally working," Dabbous said. "Yes, it has some limitations. But it's increasing the survivability of the woman through early detection."
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