A new, focused ultrasound technique seems to destroy floating tumor cells without harming nearby healthy cells.

Focused ultrasound therapy is already used against some types of tumors, with most approaches using high-intensity beams to heat and destroy the cells. But the existing methods are limited in their application and can destroy healthy cells, too. By lowering ultrasound intensity and fine-tuning its frequency, California researchers were able to break apart floating tumor cells but leave nearby healthy cells undamaged.

The key is to determine the frequency of the ultrasound wave that will destroy the dangerous cells. The proper frequency is related to the cell’s physical makeup. With different physical makeup, tumor and noncancerous cells will respond differently to the same ultrasound frequency.

In the California experiments, the researchers tried different frequencies to determine the right ones to use. Targets included leukemia, colon cancer and breast cancer cells. Neighboring healthy cells were a mix of red blood cells and immune cells.

The method, called low-intensity pulsed ultrasound, or LIPUS [lip-us], worked best against cancer cells floating among the blood cells. It didn’t work as well when the cancer cells were suspended in a gel substance.

These experiments involved cells in laboratory environments, not actual patients. Further research will require trials with patients to verify safety and efficacy. But if those experiments are successful, LIPUS could join chemotherapy, immunotherapy, radiation and surgery as a strategic weapon in the fight against cancer.