Screening mammography every two years for women ages 66 to 89 is just as beneficial as annual screening exams, regardless of whether the women have comorbidities. What's more, less frequent screening reduces false-positive rates by 19 percentage points, according to a study published in the Journal of the National Cancer Institute.
In a study that focused on the appropriateness of screening for women who might have underlying illnesses, Dejana Braithwaite, PhD, and colleagues from the University of California, San Francisco (UCSF) found that annual screening for older women does not lead to a better balance of benefits versus harms (JNCI, February 5, 2013).
Dejana Braithwaite, PhD, from UCSF."As is the case in younger women, most older women who undergo annual mammography are at high risk of false-positive mammography results and biopsy recommendations without added benefit from more frequent screening," Braithwaite and colleagues wrote.
Uncertainty over mammography
There's uncertainty about the appropriate use of screening mammography among older women because the presence of additional illnesses may diminish screening's benefits, the group said. Current guidelines reflect this: The U.S. Preventive Services Task Force (USPSTF) recommends biennial screening for women ages 50 to 74, while the American Cancer Society recommends annual screening for women older than 40, with no upper age limit.
"Although some observational studies suggest that mammography screening may benefit healthy older women, the benefit may not apply to individuals with severe comorbidity," Braithwaite and colleagues wrote. "Women who may not benefit should be spared the potential harms associated with screening, including anxiety associated with detection of nonbiologically life-threatening lesions."
Study data were collected from four Breast Cancer Surveillance Consortium (BCSC) mammography registries that shared BCSC records and Medicare claims data between January 1999 and December 2006. The data included 2,993 older women with breast cancer and 137,949 without breast cancer.
Braithwaite's group used logistic regression analyses to calculate the odds of advanced-stage, large tumors (> 20 mm), and the 10-year cumulative probability of false-positive mammography by screening frequency, age, and comorbidity score.
Tumor characteristics did not differ on a statistically significant basis by interval, age, or comorbidity, according to the researchers. Women without additional illness had invasive cancer rates of 81.6% at one-year screening and 80.1% at the two-year interval, while women with comorbidity had rates of 77.8% at one-year screening and 76.9% at the two-year interval.
But the probability of a false-positive mammography result was higher among women who were screened annually compared to those screened every other year, and the trend held regardless of whether women had additional disease: 48% of women screened annually ages 66 to 74 years had a false-positive result, compared with 29% of those screened every two years.
For women ages 75 to 89 years with comorbidity, false-positive rates were 48.4% with annual screening and 27.4% with biennial screening (women in this age group without additional disease had slightly lower estimates).
Implementing annual screening of women with comorbidities could have serious health policy implications, according to the authors. Using U.S. Census Bureau data, the UCSF team estimated there are 4.9 million U.S. women ages 66 to 89 years in the population with comorbidities and 14.3 million women without comorbidities.
"If these women undergo annual instead of biennial mammography, this could result in approximately 1 million additional false-positive examinations and 0.29 million additional false-positive biopsy recommendations among women with comorbidity plus 2.86 million additional false-positive examinations and 0.86 million additional false-positive biopsy recommendations among women without comorbidity," Braithwaite and colleagues wrote. "Thus, if older women undergo annual screening without consideration of the presence of comorbidity, it could result in substantial morbidity from screening mammography."
Are these false-positive results a problem, though? And how does undergoing annual screening without consideration of additional disease result in substantial morbidity?
"False positives are anxiety-provoking, particularly in older women who have other health problems," Braithwaite told AuntMinnie.com. "What we are saying is that if older women with comorbidity also have annual screening for breast cancer, there is potentially additional morbidity from the procedure. Undergoing a biopsy [as a result of a false-positive mammogram] could create additional complications in women who have certain conditions such as cardiovascular disease or severe diabetes."
For older women, biennial screening mammography is associated with similar rates of advanced-stage disease and lower cumulative rates of false-positive recall and biopsy recommendations as annual screening, regardless of comorbidity, Braithwaite and colleagues concluded.
"There was no difference in rates of late-stage cancer between women with breast cancer who were screened every two years compared to those who were screened every year," Braithwaite told AuntMinnie.com. "Being screened every year doesn't protect you -- it just increases your probability of a false-positive result."
