From a CalTech news article (February 4, 2020):
The hope, Lee says, is that ultrasound will kill cancer cells in a specific way that will also engage the immune system and arouse it to attack any cancer cells remaining after the treatment.
A new technique could offer a targeted approach to fighting cancer: low-intensity pulses of ultrasound have been shown to selectively kill cancer cells while leaving normal cells unharmed.
Ultrasound waves—sound waves with frequencies higher than humans can hear—have been used as a cancer treatment before, albeit in a broad-brush approach: high-intensity bursts of ultrasound can heat up tissue, killing cancer and normal cells in a target area. Now, scientists and engineers are exploring the use of low-intensity pulsed ultrasound (LIPUS) in an effort to create a more selective treatment.
A study describing the effectiveness of the new approach in cell models was published in Applied Physics Letters on January 7. The researchers behind the work caution that it is still preliminary—it still has not been tested in a live animal let alone in a human, and there remain several key challenges to address—but the results so far are promising.