Contrast-Aided Diagnostic Ultrasound Does Not Enhance Lung Metastasis in a Mouse Melanoma Tumor Model

Abstract

Objectives The purpose of this research was to test the hypothesis that contrast‐aided diagnostic ultrasound (CADUS) could exacerbate the metastatic spread of mouse melanoma tumor cells to the lungs. Methods The melanoma cell lines B16 and B16‐D5 (metastatic specifically to lung) were implanted on a hind leg of female C57/bl6 mice. Growing tumors were scanned by 1.5‐MHz diagnostic ultrasound in a 37°C water bath. Four hundred image frames were triggered at a 1‐Hz rate with 4 retro‐orbital injections of an ultrasonographic contrast agent at dosage of 10 μL/kg at 100‐second intervals. Sham‐treated mice received 400 frames of ultrasonography followed by the contrast agent with the ultrasound off. The primary tumor was surgically removed 1 day after ultrasound administration. Lungs were removed and evaluated blind after 2 weeks of bleaching in Fekete solution. Results Three experiments were performed. The first experiment involved scanning sham and CADUS groups of 20 mice each with B16 tumors; B16 metastasis was not enhanced. The second experiment repeated this test with the D5 cell line; the metastasis enhancement was marginally significant for average number (0.3 and 3.2; P = .06) and incidence (3 and 9 of 19; P = .08) in mice without tumor recurrence. Finally, a third experiment was performed to clarify ambiguous results in the second experiment and consisted of 2 groups of 40 mice each. In this larger experiment, the results were essentially equal for the sham and CADUS groups. Conclusions Overall, the results do not support the hypothesis of CADUS‐enhanced metastasis.