The finding highlights the need for continued mammography screening.
Michael S. Simon, M.D., M.P.H., leader of the breast multidisciplinary team at Barbara Ann Karmanos Cancer Institute in Detroit, Mich., and professor of internal medicine and oncology at Wayne State University School of Medicine, said:
"We found that for women age 75 and older, a longer time interval between the last mammogram and the date of breast cancer diagnosis was associated with a greater chance for dying from breast cancer."
In order to assess whether the time between mammograms had any effect on mortality, the researchers analyzed a total of 8,663 women who had been diagnosed with breast cancer for a duration of 12.2 years.
They identified an increase in the prevalence of advanced-stage disease among women who had their mammograms every five years or more compared to those who had them in intervals of six months to a year.
The researchers found that a longer time between breast cancer diagnosis and receiving a mammogram was associated with a higher risk of mortality.
Compared to women who had an interval of six months to a year between mammogram and diagnosis, women who never had a mammogram or who had one in an interval of more than five years after diagnosis were at a three times greater risk of breast cancer death.
"I am not sure why we are seeing these results particularly for older women. Tumors of younger women were more likely to be a little more unfavorable overall. It is possible that the differences in the relationship between screening interval and mortality in older versus younger women may be related to the more aggressive nature of the tumors in younger women, which might obliterate the effects of more screening. Other reasons may include differences in cancer treatment, information that was not available for this cohort of women."
The researchers conclude that it's vital that doctors discuss the risks and benefits of mammography among older patients and encourage screening. "Our findings suggest that regular mammography should be continued for older women every one or two years; however, as with younger women, mammography screening should be considered in light of the overall health of the individual woman."
In another study, researchers from the University of California, San Francisco, reported in the Journal of the National Cancer Institute (February 2013 issue) that receiving a mammogram every two years is as advantageous for older women as having one every year. They also found that biennial screening resulted in considerably fewer false positives.
Lead researchers, Dejana Braithwaite, PhD, said "Screening every other year, as opposed to every year, does not increase the probability of late-stage breast cancer in older women. Moreover, the presence of other illnesses such as diabetes or heart disease made no difference in the ratio of benefit to harm."