EFFECTS OF CONTINUOUS THERAPEUTIC ULTRASOUND ON GROWTH AND METASTASISOF SUBCUTANEOUS MURINE TUMORS

Background and Purpose. The use of therapeutic ultrasound (US) in the presence of malignant neoplasms has been contraindicated in physical t herapy practice despite a lack of convincing scientific evidence. Some studies have shown that high levels of US, which increase tissue temp eratures greater than 42-degrees-C, can kill tumors. We sought to dete rmine whether the application of continuous therapeutic US would alter the growth or metastasis of methylcholanthrene-induced solid tumors i n mice. Subjects. Seventy-one female C57BL/6 mice, age 6 to 8 weeks, r eceived subcutaneous injections of 5 x 10(5) tumor cells. Methods. Whe n tumors grew to 0.5 cm in diameter, the mice were randomly assigned t o either a control group (n=34) or an experimental group (n=37). The e xperimental group received 10 treatments over a 2-week period of 3-MHz continuous US at 1.0 W/cm2 for 5 minutes, using a 0.5-cm2 sound head directly over the tumor. The control group received the same handling except for the US treatment. Tumor dimensions were measured on days 1 (baseline), 7 (midtreatment), and 14 (preexcision and postexcision). T umors were weighted after excision, and the mice were evaluated by nec ropsy and histopathology of regional lymph nodes. Results. All tumors grew larger over time, but final tumor volume and weight were larger i n the experimental group (789 mm3 and 0.932 g) than in the control gro up (395 mm3 and 0.506 g). No significant difference existed in the num ber of metastatic lymph nodes between groups. Conclusion and Discussio n. Continuous therapeutic US increased the volume and weight of subcut aneous murine tumors in mice. We urge caution in the use of continuous therapeutic US in the areas of tumors or suspected tumors.