Injecting oxygen-filled microbubbles into breast cancer may make tumors three times more responsive to radiation treatment, according to an International Journal of Radiation Oncology study.

Researchers from Thomas Jefferson University in Philadelphia conducted the study in mice, in which the microbubbles were popped immediately before radiation treatment. The technique nearly doubled the survival time in mice from 46 days with the placebo of nitrogen-filled microbubbles, to 76 days with oxygen-filled bubbles.

"Finding a way to reverse oxygen deficiency in tumors has been a goal in radiation therapy for over 50 years," said senior author John Eisenbrey, PhD, an assistant professor of radiology at Thomas Jefferson University in a university release. "We've demonstrated here that oxygen microbubbles flush tumors with the gas and make radiation therapy significantly more effective in animal models."

Solid tumors are usually oxygen deficient and therefore more resistant to radiation. Using this approach, microbubbles are popped locally to raise the oxygen level in the tumor. However, researchers found oxygen levels increased throughout the entire cancer mass, even in areas without direct access to blood vessels.

Although the research was completed in animal subjects, a team at the Sidney Kimmel Cancer Center—part of Thomas Jefferson University—is currently using an FDA-approved microbubble contrast agent to pop microbubbles in patients with liver cancer along with radioembolization therapy. Though these bubbles aren’t filled with oxygen, the effect on the tumor still produces therapeutic benefit over therapy alone.

"The very act of bursting these microbubbles within the tumor tissue seems to change the local physiology of the tumor and make cells generally more permeable to oxygen and potentially to chemotherapy as well," said Eisenbrey. "We think this is a promising approach to test in patients to amplify the effects of radiation therapy."