The use of screening mammography CAD among Medicare patients is associated with increased incidence of ductal carcinoma in situ (DCIS), diagnosis of earlier stage breast cancer and additional downstream testing, according to a study published April 15 in Annals of Internal Medicine.

Although CAD has been widely adopted, questions about its effectiveness and clinical utility linger. Joshua J. Fenton, MD, MPH, from the Center for Healthcare Policy and Research at University of California, Davis, and colleagues sought to determine links between CAD use during screening mammography and the incidence of DCIS and invasive breast cancer, invasive cancer stage and diagnostic testing among Medicare enrollees.

The researchers mined the Surveillance, Epidemiology and End Results (SEER)-Medicare database and identified 163,099 enrollees who underwent 409,459 screening mammograms from 2001 to 2006. Women were observed for up to one year, or until repeat mammography, and for 90 days for diagnostic testing.

Use of CAD swelled from 3.6 percent of mammograms in 2001 to 60.5 percent in 2006, and CAD was associated with slightly greater incidence of breast cancer. However, women who underwent screening CAD had a greater rate of DCIS diagnosis, which accounted for the difference in incidence.

A total of 97.3 percent of women diagnosed with DCIS underwent treatment. DCIS, according to the researchers, represents a double-edged sword. “Treatment of DCIS detected by CAD may prevent progression to lethal invasive breast cancer and may avert more extensive treatment of invasive cancer.” On the flip side, they referred to research suggesting one in four cases of screen-detected and treated breast cancer occur in women who would have died of other causes. This observation may be magnified among elderly women, they added.

Fenton et al also reported greater incidence of stage I invasive breast cancer with CAD relative to mammography without CAD, and lower incidences of stage II to IV invasive disease in women who underwent mammography with CAD.

Women who were not diagnosed with breast cancer who received screening mammography with CAD had greater adjusted odds of downstream testing, including diagnostic mammography, breast ultrasound and breast biopsy than those who underwent mammography without CAD.

The researchers acknowledged the challenges of assessing CAD effectiveness, and wrote, “Weighing the potential benefits and harms of CAD use is complex, particularly because mortality benefits of screening interventions likely require many years to emerge.”

Fenton et al concluded with a call to arms. “The long-term effect of CAD on breast cancer stage, mortality, quality of life, and costs warrants investigation.”