Non-invasive evaluation of axillary lymph node status in breast cancer patients using shear wave elastography

Less invasive procedures are currently required to examine the axillary lymph node status. Shear wave elastography with acoustic radiation force impulse provides objective and reproducible quantification of the intrinsic property of the soft tissue. In this study, we measured shear wave velocity of the axillary lymph nodes of patients with breast cancer using Virtual Touch Tissue Quantification (VTTQ). The degree of lymph node metastasis was evaluated by measuring the expression level of cytokeratin 19 (CK19) mRNA, a specific marker for breast cancer cells. The one-step nucleic acid amplification (OSNA) was used to determine the copy number of CK19 mRNA in 149 lymph node specimens of 149 primary breast cancer patients. Axillary lymph node status according to OSNA (copy number/μl) were categorized as 0-249 copies (-), 250-5,000 copies (+), and copy number > 5,000 (++). A category (-) represents no metastasis in the axillary lymph node. There were 121 patients with OSNA-, 9 with OSNA+ and 19 with OSNA++. The average velocities according to OSNA categories were 1.64 ± 0.42 m/second for OSNA-, 2.25 ± 0.78 m/second for OSNA+, and 2.79 ± 0.98 m/second for OSNA++. There were significant differences in the shear wave velocity between OSNA- and OSNA+ (P = 0.040) or OSNA++ (P < 0.001). The most optimal cutoff velocity to distinguish benign from metastasis is 1.44 m/second, as determined using the receiver operating characteristic method. The shear wave velocity measured with VTTQ could provide clinically useful information about axillary lymph node metastasis in patients with primary breast cancer.