Cancer therapy with ultrasound: A historical review

The 45-year history of research in cancer therapy involving ultrasound may be divided into the four periods of initiation, enthusiasm, pessimism, and revival. There have been three approaches to the subject: studies have sought to measure the effects on tumors of (a) ultrasound alone, (b) ultrasound in combination with radiotherapy, and (c) ultrasound in combination with chemotherapy. With the first approach the results have varied. In some cases, decreased growth rates or regressions of tumors have been reported; in other cases, either no effect has been observed or growth has been increased. With the second approach, for some tumors, combined treatment has produced greater effects on tumors than has x-ray alone, whereas in other tumors the addition of ultrasound has produced no change. With the third approach, enhancement of the effects of drugs has been observed in melanoma and mouse tumor cells treated with ultrasound and several anticancer drugs. The mechanism of action in most (but not all) cases has appeared to be absorption heating. The potential of ultrasound to provide local tumor control and to enhance other therapy modes has motivated the current efforts by several groups to further study and understand its actions on malignancies.