Biennial vs. annual mammography in older women doesn't appear to alter disease-stage diagnoses

Women age 66 to 89 years who undergo biennial screening mammography have similar risk of advanced-stage disease and lower cumulative risk of a false-positive mammography study than those who are screened annually, regardless of comorbidity, a study found.

Researchers sought to evaluate the impact of biennial versus annual mammographic screening in older women, and specifically whether the stage of disease detected using this screening pattern would be affected by the presence of comorbid illness in this population.

Data were prospectively collected on 2,993 older women age 66 to 89 with invasive breast cancer or ductal carcinoma in situ and 137,949 older women without breast cancer who underwent mammography from January 1999 to December 2006, and were then matched to Medicare claims. The presence of comorbid illness in both groups was quantified using the Charlson index, a method that assigns a weighted score to specific medical conditions and provides an indicator of disease burden; patients with a Charlson score of 0 in the study were considered to have no comorbid illness present.

Study results were published online Feb. 5 by the Journal of the National Cancer Institute.

The proportion of women with adverse tumor characteristics was similar among patients screened annually and biennially, and there were no more adverse tumor characteristics at diagnosis associated with less frequent screening. Additionally, there was no association of tumor stage in patients with comorbid illness versus those without comorbidities as assessed by the Charlson index, in contrast with previous studies.

Cumulative probability of a false-positive result over 10 years of screening in women at the lower age range of the study group (66 to 74 years) was higher among those screened annually than among those screened biennially regardless of comorbidity: 48% (95% CI, 46.1% to 49.9%) of women screened annually would have a false-positive result compared with 29.0% (95% CI, 28.1% to 29.9%) of those screened biennially.

Among women at the higher age range of the study group (75 to 89 years) with comorbidity, the rate of false-positives was 48.4% (95% CI, 46.1% to 50.8%) with annual screening and 27.4% (95% CI, 26.5% to 28.4%) with biennial screening. Slightly lower estimates were obtained for women in this age group with no comorbidity.

Researchers noted that there are 4.9 million U.S. women age 66 to 89 years with comorbidities and 14.3 million women without comorbidities. They concluded, “If these women undergo annual instead of biennial mammography, this could result in approximately one 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. Thus, if older women undergo annual screening without consideration of the presence of comorbidity, it could result in substantial morbidity from screening mammography.”

The authors also noted that a randomized, controlled trial of mammography in older women is unlikely to be performed, and therefore more high-quality observational studies that look at additional measures of comorbidity and breast cancer mortality “may facilitate improved understanding of the benefits and harms of different screening mammography frequencies among older women and, ultimately, inform clinical and policy decisions about the appropriate use of screening in this growing population.”