In a sample group of more than 64,000 elderly women who had mammograms from 1995 to 2009, those who self-selected for annual mammography had lower 10-year breast cancer mortality than those who opted for biennial, irregular or no exams.
Charles Hennekens, MD, of Florida Atlantic University, and colleagues analyzed data from Medicare claims linked to the National Cancer Institute’s SEER program. Their study was published in the December edition of the American Journal of Medicine.
Ascertaining all primary breast cancer cases diagnosed between ages 69 and 84 years, the researchers looked at screening mammography patterns during the four years prior to the year of diagnosis in the group of women (59,498 non-Hispanic white and 4,886 black).
They recorded mortality caused by breast cancer during the 10 years immediately after diagnosis, adjusting for cancer stage at diagnosis, radiation therapy, chemotherapy, comorbid conditions and contextual socioeconomic status.
The team found that hazard ratios for breast cancer mortality relative to no/irregular mammography at 10 years for women aged 69 to 84 years at diagnosis were similarly striking across racial lines:
- 0.31 (0.29-0.33) for annual mammography and 0.47 (0.44-0.51) for biennial mammography among whites; and
- 0.36 (0.29-0.44) for annual mammography and 0.47 (0.37-0.58) for biennial mammography among blacks.
Trends were similar at five years overall, while 69- to 84-year-old women receiving regular annual screening mammography had consistently lower five-year and 10-year risks of breast cancer mortality than women with no or irregular screening, regardless of race.
Additionally, 10-year risks were more than three times higher among white women and more than two times higher among black women aged 69 to 84 years with no or irregular screening compared with annual screening.
To measure potential harm from mammography screening, the researchers calculated the percentage of women who received breast biopsies after false-positive diagnoses.
Among whites in this subgroup, there were 288 biopsies among the 11,452 women receiving annual mammography (2.5 percent) that would not have occurred with biennial screening.
Among blacks, there were 35 biopsies among the 1,277 women receiving annual mammography (2.7 percent) that would not have occurred with biennial screening.
The net increase for annual screening was 323 biopsies among the 54,213 women receiving annual or biennial mammography (0.6 percent).
The authors concluded by noting that, in 2010, there were 19.2 million women aged 65 to 84 years residing in the U.S., and they accounted for 41 percent of all U.S. breast cancer deaths during that year.
“We believe the current evidence about potential benefits and harms from screening mammography in this population is insufficient for clinical or policy decisions,” they write. “The need for better data is reflected by the magnitude of breast cancer as a cause of death among the elderly, the likelihood of greater numbers of women living to advanced age, and the projections indicating that racial and ethnic minorities will comprise 28 percent of the U.S. elderly population aged 65 years or more by the year 2030.”
Although a large-scale randomized trial comparing the risks and benefits of annual vs. biennial mammography in the elderly would be hampered by high costs and feasibility issues, they add, this design strategy “would provide the most reliable means to assess the most plausible way to discriminate small to moderate differences.
“In the interim, the present results highlight the evidentiary limitations of data used for current screening mammography recommendations.”