Previous population-based studies comparing the accuracy of SFM versus FFDM have reported conflicting results, and reported recall ratesor the rate at which women are called back for additional testshave varied widely. In addition, past performance evaluations of breast imaging screening technologies do not account for the transition phase of adoption.
For this study, data collected from the Norwegian Breast Cancer Screening Program (NBCSP) was used to compare performance measures and outcomes before, during and after the transition from SFM to FFDM.
"The program invites women age 50 to 69 years to mammographic screening every two years," said Solveig Hofvind, Ph.D., from the Cancer Registry of Norway and Oslo University College, in Oslo, Norway. "We analyzed performance measures in the program as run in a usual setting."
To examine the effect of transition from SFM to FFDM, researchers analyzed the rate of cases, the recall rate, the rate of screen-detected cancer, and the rate of interval cancers.
"The study includes results from women screened with SFM only, with both SFM and FFDM, and with FFDM only. These combinations make us able to compare early performance measures achieved when using digital mammography in a routine setting, in a proper way," Dr. Hofvind said.
A total of 1,837,360 NBCSP screening exams were performed from 1996 through 2010, with 58.8 years being the average age at the time of screening. The overall recall rate was 3.4 percent for SFM and 2.9 percent for FFDM. The biopsy rate was 1.4 percent for SFM and 1.1 percent for FFDM.
Both the rate of invasive screening-detected and interval breast cancer remained stable during the transition from SFM to FFDM and after FFDM was firmly established. The positive predictive value of recalled examinations and of biopsy procedures increased from 19.3 percent and 48.3 percent to 22.7 percent and 57.5 percent, respectively, after adoption of FFDM.
By studying the transition phase of screening modality, researchers discovered FFDM implementation led to lower rates of false positive screening exams and fewer biopsies with benign outcome.