Tumor stiffness measured by shear wave elastography correlates with tumor hypoxia as well as histologic biomarkers in breast cancer

Abstract

Background: Shear wave elastography (SWE) is an ultrasound technique for the noninvasive quantification of tissue stiffness. The hypoxic tumor microenvironment promotes tumor stiffness and is associated with poor prognosis in cancer. We aimed to investigate the correlation between tumor hypoxia and histologic biomarkers and tumor stiffness measured by SWE in breast cancer.

Methods: From June 2016 to January 2018, 82 women with invasive breast cancer who underwent SWE before treatment were enrolled. Average tumor elasticity (E_average) and tumor-to-fat elasticity ratio (E_ratio) were extracted from SWE. Immunohistochemical staining of glucose transporter 1 (GLUT1) was used to assess tumor hypoxia in breast cancer tissues and automated digital image analysis was performed to assess GLUT1 activities. Spearman correlation and logistic regression analyses were performed to identify associations between GLUT1 expression and SWE values, histologic biomarkers, and molecular subtypes. The Mann-Whitney U test, t test, or Kruskal-Wallis test was used to compare SWE values and histologic features according to the GLUT1 expression (≤the median vs > median).

Results: E_average (r = 0.676) and E_ratio (r = 0.411) correlated significantly with GLUT1 expression (both p < 0.001). E_average was significantly higher in cancers with estrogen receptor (ER)-, progesterone receptor (PR)-, Ki67+, and high-grade (p < 0.05). E_ratio was higher in cancers with Ki67+, lymph node metastasis, and high-grade (p < 0.05). Cancers with high GLUT1 expression (>median) had higher E_average (mean, 85.4 kPa vs 125.5 kPa) and E_ratio (mean, 11.7 vs 17.9), and more frequent ER- (21.7% vs 78.3%), PR- (26.4% vs 73.1%), Ki67+ (31.7%% vs 68.3%), human epidermal growth factor receptor 2 (HER2) + (25.0% vs 75.0%), high-grade (28.6% vs 71.4%), and HER2-overexpressing (25.0% vs 75.0%) and triple-negative (23.1% vs 76.9%) subtypes (p < 0.05). Multivariable analysis showed that E_average was independently associated with GLUT1 expression (p < 0.001).

Conclusions: Tumor stiffness on SWE is significantly correlated with tumor hypoxia as well as histologic biomarkers. In particular, E_average on SWE has independent prognostic significance for tumor hypoxia in the multivariable analysis and can potentially be used as a noninvasive imaging biomarker to predict prognosis and pretreatment risk stratification in breast cancer patients.

Keywords: Biomarkers; Breast cancer; Elastography; Hypoxia; Tumor microenvironment; Ultrasonography.

Fig. 1

Flowchart of patients included

Fig. 2

Quantitative measurement of tumor stiffness on shear-wave elastography (SWE) and immunohistochemical staining. a. Quantitative elasticity parameters were measured on the elasticity color map image. Two round 2-mm-diameter regions of interests were positioned on the hardest part of the mass and adjacent adipose tissue. The ultrasound system automatically displayed average elasticity of the tumor (E_average) with standard deviation, average elasticity of the adjacent fat with standard deviation, and elasticity ratio between the tumor’s average elasticity and the average elasticity of adjacent fat (E_ratio). Two quantitative SWE parameters, E_average (yellow box) and E_ratio (green box), were extracted to investigate the relationships between stiffness parameters on SWE and immunohistochemical staining. b–c. On immunohistochemical staining, the area fraction of positive reactions was measured. Each color image was converted to a binary image. The positive areas—brown area for glucose transporter-1 protein (GLUT1) staining (× 100) (b)—were converted to red (c). The area fraction of positive GLUT1 reaction was determined as the percentage of red pixels in the binary image