The Breast Tumor Strain Ratio Is a Predictive Parameter for Axillary Lymph Node Metastasis in Patients With Invasive Breast Cancer

OBJECTIVE. The purpose of this study was to evaluate the association between the breast tumor strain ratio and axillary lymph node metastasis in patients with invasive breast cancer. MATERIALS AND METHODS. The records of 284 patients with invasive breast cancer who underwent ultrasound elastography before surgery between March 2013 and May 2014 were reviewed retrospectively. For women with multifocal or bilateral cancer, the largest tumor was included. An experienced radiologist performed ultrasound elastography and measured the strain ratio, which is defined as the fat-to-lesion ratio and is indicative of the relative stiffness of the breast lesion, using dedicated software within the ultrasound equipment. The associations between axillary lymph node metastasis with the tumor strain ratio and clinical and biologic variables were evaluated using univariate and multivariate logistic regression analyses. RESULTS. Among 284 tumors, 85 (29.9%) showed axillary lymph node metastasis by surgical histopathologic analysis. The strain ratio was statistically significantly higher in tumors with axillary lymph node metastasis than in those without axillary lymph node metastasis (mean +/- SD, 5.19 +/- 1.28 vs 4.17 +/- 1.30, respectively; p < 0.001). On univariate analysis, a higher strain ratio (> 3.89), larger tumor size (> 2 cm), higher histologic grade (grade 3), presence of lymphovascular invasion, palpability, and higher expression of Ki-67 (>= 14%) were statistically significantly associated with axillary lymph node metastasis. On multivariate analysis, a higher strain ratio (> 3.89) (odds ratio [OR], 14.208; p < 0.001), presence of lymphovascular invasion (OR, 17.437; p < 0.001), and higher expression of Ki-67 (>= 14%) (OR, 3.744; p = 0.002) maintained independent significance for predicting axillary lymph node metastasis. CONCLUSION. The breast tumor strain ratio on ultrasound elastography is associated independently with axillary lymph node metastasis in patients with invasive breast cancer.