Effects of continuous therapeutic ultrasound on growth and metastasis of subcutaneous murine tumors.

BACKGROUND AND PURPOSE

The use of therapeutic ultrasound (US) in the presence of malignant neoplasms has been contraindicated in physical therapy practice despite a lack of convincing scientific evidence. Some studies have shown that high levels of US, which increase tissue temperatures greater than 42 degrees C, can kill tumors. We sought to determine whether the application of continuous therapeutic US would alter the growth or metastasis of methylcholanthrene-induced solid tumors in mice.

SUBJECTS

Seventy-one female C57BL/6 mice, age 6 to 8 weeks, received subcutaneous injections of 5 x 10(5) tumor cells.

METHODS

When tumors grew to 0.5 cm in diameter, the mice were randomly assigned to either a control group (n = 34) or an experimental group (n = 37). The experimental 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). Tumors were weighed after excision, and the mice were evaluated by necropsy and histopathology of regional lymph nodes.

RESULTS

All tumors grew larger over time, but final tumor volume and weight were larger in the experimental group (789 mm3 and 0.932 g) than in the control group (395 mm3 and 0.506 g). No significant difference existed in the number of metastatic lymph nodes between groups.

CONCLUSION AND DISCUSSION

Continuous therapeutic US increased the volume and weight of subcutaneous murine tumors in mice. We urge caution in the use of continuous therapeutic US in the areas of tumors or suspected tumors.