Therapeutic Ultrasound and the Metastasis of a Solid Tumor

Therapeutic ultrasound applied over tumors is thought to promote metastasis. This study was completed to test the hypothesis that repeated application of therapeutic ultrasound accelerates the spread of malignant tumors. Forty mice with subcutaneous Lewis lung cell tumors were assigned as control, sham, or treated animals. Treatment animals were given 5 min of pulsed or continuous ultrasound over the tumors for 6 consecutive days. The mice were sacrificed, the tumors and lungs were removed, and the tissue was examined for evidence of metastasis. A significant increase in the number of metastases was observed in animals treated with continuous (p < .001) and pulsed ultrasound (p < .01). The study provides experimental evidence supporting the clinical advice that therapeutic ultrasound should not be applied to tumors.