Canine Mammary Tumors: Predicting Malignancy Using Ultrasonography

Radiologists use ultrasonography along with other imaging methods to evaluate breast tumors in women. In a study published last month in PLOS One, researchers in Brazil evaluated 4 ultrasonography techniques for assessing mammary tumors in dogs. Their results indicate that acoustic radiation force impulse (ARFI) elastography can be an effective predictor of malignancy in canine mammary tumors.

“Several reports have demonstrated the applicability and limitations of B-mode ultrasonography, Doppler, elastography, and contrast-enhanced ultrasonography (CEUS) in the evaluation of breast cancer in humans and canines,” write the authors. “However, no report has yet compared the efficacy of these ultrasonography techniques in predicting malignancy of mammary tumors.”

The prospective study included 300 mammary masses from 153 client-owned dogs seen at the veterinary teaching hospital at Universidade Estadual Paulista, São Paulo, from 2014 to 2016. A veterinary sonographer evaluated the tumors with each of the 4 techniques before the dogs underwent mastectomy.

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Definitive diagnoses were made with histopathology after mass excision. Of the 300 tumors, 246 (82%) were classified as malignant and 54 (18%) were classified as benign on histopathology.

B-mode Ultrasonography

B-mode (conventional) ultrasonography reveals a tumor’s size, margins, echogenicity, echotexture, and invasiveness. In this study, malignant tumors were larger than benign tumors on B-mode ultrasonography. The sensitivity, specificity, and accuracy of certain tumor dimensions measured by this technique were judged moderate for predicting malignancy. For other tumor characteristics, this technique was not effective in differentiating malignant from benign masses.

Doppler Imaging

Doppler color flow imaging is used to assess a tumor’s blood supply. Spectral Doppler vascular indexes can help distinguish malignant from benign mammary masses in humans, say the authors. In this study, vascular indexes measured by Doppler ultrasonography had moderate sensitivity, specificity, and accuracy for predicting malignancy in canine mammary tumors.

Contrast-enhanced Ultrasonography

CEUS was performed after intravenous administration of sulfur hexafluoride contrast material. This technique allows visualization of smaller blood vessels than can be seen with color Doppler imaging, and the degree of contrast enhancement is considered an indicator of malignancy or benignity in humans. In this study, although CEUS revealed macro- and microcapillarization of tumors, none of the measured parameters correlated significantly with malignancy. The authors judged the sensitivity of this technique to be high but the specificity to be low for predicting malignancy.

Elastography

Elastography is a relatively new technique that measures the deformability of a mass (the elasticity vs rigidity of the tissue). Mammary carcinomas are more rigid than benign masses because of increased stromal collagen levels, say the authors. In this study, ARFI elastography characteristics were similar to those previously reported in humans and dogs. The mean shear wave velocity measured by this technique was 95% accurate in predicting malignancy.

ARFI elastography is “an exceptionally effective technique for malignancy prediction in canine mammary masses,” write the authors. “Based on the results from this study, quantitative ARFI elastography proved to be the best method of ultrasonographic prediction of malignancy in mammary masses,” they add. They recommend ARFI elastography as a rapid, noninvasive method of predicting mammary mass malignancy in dogs.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.