What are the characteristics of breast cancers misclassified as benign by quantitative ultrasound shear wave elastography?

Shear wave elastography (SWE) is a promising adjunct to greyscale ultrasound in differentiating benign from malignant breast masses. The purpose of this study was to characterise breast cancers which are not stiff on quantitative SWE, to elucidate potential sources of error in clinical application of SWE to evaluation of breast masses. Three hundred and two consecutive patients examined by SWE who underwent immediate surgery for breast cancer were included. Characteristics of 280 lesions with suspicious SWE values (mean stiffness > 50 kPa) were compared with 22 lesions with benign SWE values (< 50 kPa). Statistical significance of the differences was assessed using non-parametric goodness-of-fit tests. Pure ductal carcinoma in situ (DCIS) masses were more often soft on SWE than masses representing invasive breast cancer. Invasive cancers that were soft were more frequently: histological grade 1, tubular subtype, a parts per thousand currency sign10 mm invasive size and detected at screening mammography. No significant differences were found with respect to the presence of invasive lobular cancer, vascular invasion, hormone and HER-2 receptor status. Lymph node positivity was less common in soft cancers. Malignant breast masses classified as benign by quantitative SWE tend to have better prognostic features than those correctly classified as malignant. aEuro cent Over 90 % of cancers assessable with ultrasound have a mean stiffness > 50 kPa. aEuro cent 'Soft' invasive cancers are frequently small (a parts per thousand currency sign10 mm), low grade and screen-detected. aEuro cent Pure DCIS masses are more often soft than invasive cancers (> 40 %). aEuro cent Large symptomatic masses are better evaluated with SWE than small clinically occult lesions. aEuro cent When assessing small lesions, 'softness' should not raise the threshold for biopsy.