Assessment of Tumor Stiffness With Shear Wave Elastography in a Human Prostate Cancer Xenograft Implantation Model.

OBJECTIVES

To investigate the stiffness of human prostate cancer in a xenograft implantation model using shear wave elastography and compare the pathologic features of tumors with varying elasticity.

METHODS

Human prostate cancer DU-145 cells were injected into 24 nude male mice. The mice were divided into 3 groups according to the time of transplantation (6, 8, and 10 weeks). The volume, elasticity, and Young modulus of tumors were recorded by 2-dimensional sonography and shear wave elastography. The tumors were collected for pathologic analyses: hematoxylin-eosin staining, Ponceau S, and aniline staining were used to stain collagen and elastic fibers, and picric acid-sirius red staining was used to indicate type I and III collagen. The area ratios of collagen I/III were calculated. The correlation between the Young modulus of the tumor and area ratio of collagen I/III were evaluated. Immunohistochemistry of vimentin and α-smooth muscle actin was performed.

RESULTS

Nineteen tumors in 3 groups were collected. The volume and mean Young modulus increased with the time of transplantation. There were more collagen fibers in the stiff tumors, and there were significant differences in the area ratios of collagen I/III between groups 1 (mean ± SD, 0.50 ± 0.17) and 3 (1.97 ± 0.56; P < .01). The Young modulus of the tumors showed a very significant correlation with the area ratios of collagen I/III (r = 0.968; P < .05). The expression level of α-smooth muscle actin protein was higher in group 3 than in the other groups, but differences in vimentin expression were barely seen.

CONCLUSIONS

Shear wave elastography is a novel useful technology for showing the elasticity of human prostate cancer xenograft implantation tumors. Collagen fibers, especially collagen type I, play a crucial role in the elasticity in the human prostate cancer xenograft implantation model.