Diagnostic Performance of Point-of-Care Apparent Diffusion Coefficient Measures to Reduce Biopsy in Breast Lesions at MRI: Clinical Validation

Background: The Eastern Cooperative Oncology Group-American College of Radiology Imaging Network Cancer Research Group multicenter A6702 trial identified an optimal apparent diffusion coefficient (ADC) cutoff to potentially reduce biopsies by 21% without affecting sensitivity. Whether this performance can be achieved in clinical settings has not yet been established. Purpose: To validate the performance of point -of -care ADC measurements with the A6702 trial ADC cutoff for reducing unnecessary biopsies in lesions detected at breast MRI. Materials and Methods: Consecutive breast MRI examinations performed from May 2015 to January 2019 at a single medical center and showing biopsy -confirmed Breast Imaging Reporting and Data System category 4 or 5 lesions, without ipsilateral cancer, were identified. Point -of -care lesion ADC measurements collected at clinical interpretation were retrospectively evaluated. MRI examinations included axial T2 -weighted, diffusion -weighted, and dynamic contrast -enhanced sequences. Sensitivity and biopsy reduction rates were calculated by applying the A6702 optimal (ADC, 1.53 x 10-3 mm2/sec) and alternate conservative (1.68 x 10-3 mm2/sec) cutoffs. Lesion pathologic outcomes were the reference standard. To assess reproducibility, one radiologist repeated ADC measurements, and agreement was summarized using the intraclass correlation coefficient. Results: A total of 240 lesions in 201 women (mean age, 49 years +/- 13 [SD]) with pathologic outcomes (63 malignant and 177 benign) were included. Applying the optimal ADC cutoff produced an overall biopsy reduction rate of 15.8% (38 of 240 lesions [95% CI: 11.2, 20.9]), with a sensitivity of 92.1% (58 of 63 lesions [95% CI: 82.4, 97.4]; sensitivity was 97.2% [35 of 36 lesions] [95% CI: 82.7, 99.6] for invasive cancers). Results were similar for screening versus diagnostic examinations (P = .92 and .40, respectively). Sensitivity was higher for masses than for nonmass enhancements (NMEs) (100% vs 85.3%; P = .009). Applying the conservative ADC cutoff achieved a sensitivity of 95.2% (60 of 63 lesions [95% CI: 86.7, 99.0]), with a biopsy reduction rate of 10.4% (25 of 240 lesions [95% CI: 6.7, 14.5]). Repeated single -reader measurements showed good agreement with clinical ADCs (intraclass correlation coefficient, 0.72 [95% CI: 0.58, 0.81]). Conclusion: This study validated the clinical use of ADC cutoffs to reduce MRI-prompted biopsies by up to 16%, with a suggested tradeoff of lowered sensitivity for in situ and microinvasive disease manifesting as NME.