BOSTON -- Only a minority of older breast cancer survivors undergoes recommended yearly surveillance mammography, but for those who do, the risk of dying from the disease is cut by almost a third, researchers found.
BOSTON, July 24 -- Only a minority of older breast cancer survivors undergoes recommended yearly surveillance mammography, but for those who do, the risk of dying from the disease is cut by almost a third, researchers found.
In a large observational study, each additional surveillance mammogram for breast cancer survivors ages 65 and older was associated with a 31% lower risk of breast cancer mortality (95% confidence interval 18% to 48%), said Timothy L. Lash, D.Sc., of Boston University, and colleagues.
But, only 41% of the women had had at least four mammograms over five years of follow-up, despite access to care, they reported in the July 20 issue of the Journal of Clinical Oncology.
These results "suggest that as many as 500,000 older women will die of their breast cancers" because of suboptimal mammography surveillance, said Jeanne Mandelblatt, M.D., M.P.H., of Georgetown University in an accompanying editorial.
The American Society of Clinical Oncology recommends annual surveillance mammography for all women who survive breast cancer.
However, there has been no clinical trial evidence to support this guideline. Furthermore, older women have typically been excluded from even screening mammography trials, so it was not known whether they would benefit.
The researchers aimed to close this gap by studying 1,846 stage I and II breast cancer patients ages 65 and older who were insured through six integrated health care delivery systems in the Cancer Research Network.
The investigators reviewed medical records, examined patient databases, and checked the National Death Index. They matched each of the 178 women who died of breast cancer during the first five years of follow-up to four survivors for a total of 634 controls.
Among survivors, only 2.0% had at least four surveillance mammograms during the five years of follow-up. Over the mean 31.8 months of follow-up, 40% had no surveillance mammography and 32% had only one.
Overall, each additional surveillance mammogram was associated with a significant reduction in the likelihood of breast cancer mortality despite matched risk between groups and adjustment for change in comorbidity from baseline (odds ratio 0.69, 95% CI 0.52 to 0.92).
The mortality reduction per mammogram was even greater for the following groups:
Among women who had a local breast cancer recurrence, those who died were less likely to have had a surveillance mammogram in the prior year than those who survived (38% versus 79%, P=0.02).
As expected, "given that mammograms can only detect tumors in the breast," surveillance mammograms did not appear to have a significant effect on survival for women with regional or distant recurrences.
However, the 213 women who died from non-breast cancer causes also appeared to have a significant mortality benefit from each additional surveillance mammogram compared with their matched controls (adjusted OR 0.68, 95% CI 0.56 to 0.83).
While this may cause some skepticism that surveillance mammograms are not the real cause of the mortality benefit, the researchers noted, the test could confer benefits beyond just detection.
For example, they wrote, it may make women more aware of early signs or symptoms of recurrence, they wrote, "which may be associated with earlier detection of the recurrence and improved prognosis."
Therefore, "the reduced mortality rate likely results from the effect of detecting local recurrences or second primary breast cancer at an earlier stage with better prognosis, combined with the effect of better medical care in general," the researchers concluded.
These findings should bolster physicians' confidence in recommending and reinforcing the value of surveillance mammograms to all their patients, Dr. Mandelblatt said.
"Physician recommendation of proven effective interventions remains one of our strongest tools in the war against cancer," she added.