Quantitative Maximum Shear-Wave Stiffness of Breast Masses as a Predictor of Histopathologic Severity

OBJECTIVE. The objective of our study was to compare quantitative maximum breast mass stiffness on shear-wave elastography (SWE) with histopathologic outcome. SUBJECTS AND METHODS. From September 2008 through September 2010, at 16 centers in the United States and Europe, 1647 women with a sonographically visible breast mass consented to undergo quantitative SWE in this prospective protocol; 1562 masses in 1562 women had an acceptable reference standard. The quantitative maximum stiffness (termed "Emax") on three acquisitions was recorded for each mass with the range set from 0 (very soft) to 180 kPa (very stiff). The median Emax and interquartile ranges (IQRs) were determined as a function of histopathologic diagnosis and were compared using the Mann-Whitney U test. We considered the impact of mass size on maximum stiffness by performing the same comparisons for masses 9 mm or smaller and those larger than 9 mm in diameter. RESULTS. The median patient age was 50 years (mean, 51.8 years; SD, 14.5 years; range, 21-94 years), and the median lesion diameter was 12 mm (mean, 14 mm; SD, 7.9 mm; range, 1-53 mm). The median Emax of the 1562 masses (32.1% malignant) was 71 kPa (mean, 90 kPa; SD, 65 kPa; IQR, 31-170 kPa). Of 502 malignancies, 23 (4.6%) ductal carcinoma in situ (DCIS) masses had a median Emax of 126 kPa (IQR, 71-180 kPa) and were less stiff than 468 invasive carcinomas (median Emax, 180 kPa [IQR, 138-180 kPa]; p = 0.002). Benign lesions were much softer than malignancies (median Emax, 43 kPa [IQR, 24-83 kPa] vs 180 kPa [IQR, 129-180 kPa]; p < 0.0001). Usual benign lesions were soft, including 62 cases of fibrocystic change (median Emax, 32 kPa; IQR, 24-94 kPa), 51 cases of fibrosis (median Emax, 36 kPa; IQR, 22-102 kPa), and 301 fibroadenomas (median Emax, 45 kPa; IQR, 30-79 kPa). Eight lipomas (median Emax, 14 kPa; IQR, 8-15 kPa), 154 cysts (median Emax, 29 kPa; IQR, 10-58 kPa), and seven lymph nodes (median Emax, 17 kPa; IQR, 9-40 kPa) were softer than usual benign lesions (p < 0.0001 for lipomas and cysts; p = 0.007 for lymph nodes). Risk lesions were slightly stiffer than usual benign lesions (p = 0.002) but tended to be softer than DCIS (p = 0.14). Fat necrosis and abscesses were relatively stiff. Conclusions were similar for both small and large masses. CONCLUSION. Despite overlap in Emax values, maximum stiffness measured by SWE is a highly effective predictor of the histopathologic severity of sonographically depicted breast masses.