Relative timing of mammography and MRI for breast cancer screening: Impact on performance evaluation

Objective Mammography and MRI screening typically occur in combination or in alternating sequence. We compared multimodality screening performance accounting for the relative timing of mammography and MRI and overlapping follow-up periods. Methods We identified 8,260 screening mammograms performed 2005-2017 in the Breast Cancer Surveillance Consortium, paired with screening MRIs within +/- 90 days (combined screening) or 91-270 days (alternating screening). Performance for combined screening [cancer detection rate (CDR) per 1000 examinations and sensitivity] was calculated with one-year follow-up for each modality, and with a single follow-up period treating the two tests as a single test. Alternating screening performance was calculated with one-year follow-up for each modality and also with follow-up ending at the next screen if within one year (truncated follow-up). Results For 3,810 combined screening pairs, CDR per 1000 screens was 6.8 (95%CI: 4.6-10.0) for mammography and 12.3 (95%CI: 9.3-16.4) for MRI as separate tests compared to 13.1 (95%CI: 10.0-17.3) as a single combined test. Sensitivity of each test was 48.1% (35.0%-61.5%) for mammography and 79.7% (95%CI: 67.7-88.0%) for MRI compared to 96.2% (95%CI: 85.9-99.0%) for combined screening. For 4,450 alternating screening pairs, mammography CDR per 1000 screens changed from 3.6 (95%CI: 2.2-5.9) to zero with truncated follow-up; sensitivity was incalculable (denominator=0). MRI CDR per 1000 screens changed from 12.1 (95%CI 9.3-15.8) to 11.7 (95%CI: 8.9-15.3) with truncated follow-up; sensitivity changed from 75.0% (95%CI 63.8-83.6%) to 86.7% (95%CI 75.5-93.2%). Discussion Updating auditing approaches to account for combined and alternating screening sequencing and to address outcome attribution issues arising from overlapping follow-up periods can improve the accuracy of multimodality screening performance evaluation.