Anisotropy of Solid Breast Lesions in 2D Shear Wave Elastography is an Indicator of Malignancy

Rationale and Objectives

To investigate if anisotropy at two-dimensional shear wave elastography (SWE) suggests malignancy and whether it correlates with prognostic and predictive factors in breast cancer.

Materials and Methods

Study group A of 244 solid breast lesions was imaged with SWE between April 2013 and May 2014. Each lesion was imaged in radial and in antiradial planes, and the maximum elasticity, mean elasticity, and standard deviation were recorded and correlated with benign/malignant status, and if malignant, correlated with conventional predictive and prognostic factors. The results were compared to a study group B of 968 solid breast lesions, which were imaged in sagittal and in axial planes between 2010 and 2013.

Results

Neither benign nor malignant lesion anisotropy is plane dependent. However, malignant lesions are more anisotropic than benign lesions ( P ≤ 0.001). Anisotropy correlates with increasing elasticity parameters, breast imaging-reporting and data system categories, core biopsy result, and tumor grade. Large cancers are significantly more anisotropic than small cancers ( P ≤ 0.001). The optimal anisotropy cutoff threshold for benign/malignant differentiation of 150 kPa 2 achieves the best sensitivity (74%) with a reasonable specificity (63%).

Conclusions

Anisotropy may be useful during benign/malignant differentiation of solid breast masses using SWE. Anisotropy also correlates with some prognostic factors in breast cancer.

Introduction

Supersonic shear wave elastography (SWE) is an ultrasound imaging modality that visualizes the elasticity of tissue. It was introduced by Bercoff et al. in 2004 and has been in clinical use since 2009 . During examinations, the propagation speed of the shear wave is measured and the elasticity, represented as Young’s modulus E, is calculated as

E=3ϱc2 E

where c is the propagation speed of the shear wave and ϱ is the density of the tissue. Thus. SWE is a quantitative measurement method. The elasticity is visualized as a color map overlaying the grayscale B-mode ultrasound image of the lesion. As the shear wave is induced by applying an acoustic radiation force, there is no need to move the transducer. A good interobserver reproducibility can be achieved . Furthermore, Berg et al. have shown that analyzing the quantitative elasticity of a lesion with SWE is useful for the differentiation of benign and malignant lesions as malignant tissue is generally stiffer than benign tissue . Berg et al. recommended the use of a cutoff threshold for the maximum elasticity (E max ) of 80 kPa for the optimal benign/malignant differentiation . Evans et al. recommended a cutoff threshold for the mean elasticity (E mean ) of 50 kPa .

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Materials and Methods

Study Groups

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Ultrasound Device

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Image Evaluation

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AD=antiradial−radial A

antiradial

−

radial

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AF=(antiradial−radial)2 A

(

antiradial

−

radial

)

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AF=(sagittal−axial)2 A

(

sagittal

−

axial

)

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Statistics

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Results

Evaluation of the Study Groups

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TABLE 1

Subtypes of Solid Breast Lesions in Study Group A and Study Group B

Study Group A Study Group B Subtype Number % Number % Malignant Ductal carcinoma in situ 4 2 18 3 Ductal carcinoma of no specific type 110 66 482 74 Lobular carcinoma 34 21 78 12 Mucinous carcinoma 7 4 9 1 Tubular carcinoma 6 4 23 4 Other 5 3 52 9 Benign Fibroadenoma 44 56 148 49 Fibrocystic changes 7 9 56 18 Liponecrosis 3 4 15 5 Papilloma 2 3 14 5 Other 22 28 73 23

TABLE 2

Ultrasound Assessment and Histological Features of Study Group A and Study Group B

Study Group A Study Group B Feature Number % Number % Source Screening 75 31 339 35 Symptomatic 170 69 629 65 Imaging US size <15 mm 115 47 454 47 US size ≥15 mm 130 53 514 53 US BIRADS 3 34 14 53 11 US BIRADS 4a 25 10 68 15 US BIRADS 4b 28 11 88 19 US BIRADS 4c 70 29 109 23 BIRADS 5 88 36 152 32 E max <80 kPa 97 40 336 35 E max ≥80 kPa 148 60 615 65 E mean <50 kPa 73 30 250 26 E mean ≥50 kPa 172 70 717 74 SD <7 kPa 104 42 393 41 SD ≥7 kPa 141 58 572 59 Histology Core result B1 0 0 7 1 Core result B2 70 29 261 27 Core result B3 8 3 39 4 Core result B5a 9 4 33 3 Core result B5b 158 64 626 65 Core result B5c 0 0 2 0 Characteristics of invasive cancers HER2+ 15 10 85 13 ER+ 136 83 522 81 PR+ 111 68 437 68 Grade 1 15 9 71 11 Grade 2 85 52 274 43 Grade 3 65 39 289 46 Lymph node positive 49 38 174 31 Vascular invasion 40 31 156 28

BIRADS, breast imaging-reporting and data system; E max , maximum elasticity; E mean , mean elasticity; ER, estrogen receptor; HER2, human epidermal growth factor 2; PR, progesterone receptor; SD, standard deviation; US, ultrasound.

Size, nodal status, and vascular invasion were not available in those women treated initially with systematic therapy. HER status is missing in women with equivocal enzyme-linked immunosorbent assay (ELISA) results who were not candidates for chemotherapy.

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Plane Dependency

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Anisotropy Threshold

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TABLE 3

Diagnostic Performance of Anisotropy Factor (AF)

Threshold Study Group A Study Group B Se Sp DA Se Sp DA 150 74 63 71 72 59 68 200 70 68 69 69 62 67 250 68 71 69 68 68 68

DA, diagnostic accuracy; Se, sensitivity; Sp, specificity.

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Correlation with Source of Referral

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Correlation with Ultrasound Imaging and Elasticity Characteristics

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Correlation with Ultrasound BIRADS

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Correlation with Core Result

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Correlation with Tumor Grade

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Correlation with Other Histological Features

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Correlation with Subtypes

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TABLE 4

Correlation of AF with Tissue Subtype of the Lesions of Study Group A and Study Group B

Subtype Study Group A Study Group B AF (kPa 2 /100) AF (kPa 2 /100) Benign Fibroadenoma 5 4 Fibrocystic changes 6 13 Liponecrosis 42 4 Papilloma 6 5 Other 13 8 Malignant Ductal carcinoma in situ 26 7 Ductal carcinoma of no specific type 23 24 Lobular carcinoma 32 24 Mucinous carcinoma 5 11 Tubular carcinoma 7 15 Papillary carcinoma 2 32 Other 17 22

AF, anisotropy factor.

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Discussion

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Acknowledgment

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References

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Anisotropy of Solid Breast Lesions in 2D Shear Wave Elastography is an Indicator of Malignancy

Rationale and Objectives

Materials and Methods

Results

Conclusions

Introduction

Materials and Methods

Study Groups

Ultrasound Device

Image Evaluation

Statistics

Results

Evaluation of the Study Groups

Plane Dependency

Anisotropy Threshold

Correlation with Source of Referral

Correlation with Ultrasound Imaging and Elasticity Characteristics

Correlation with Ultrasound BIRADS

Correlation with Core Result

Correlation with Tumor Grade

Correlation with Other Histological Features

Correlation with Subtypes

Discussion

Acknowledgment

References

Further Reading

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