Researchers have been looking for years for a way to use oxygen to fight cancer. Now, they may finally have one.

A new study finds that giving high-dose oxygen may help efforts to stimulate the immune system against tumors. The study’s only been done in mice and hasn’t been shown safe in people yet — but it does open some possibilities, the researchers report in the journal Science Translational Medicine.

Treating tumors via oxygen has been attempted before but researchers wanted to try a non-toxic approach, giving a 60% oxygen mix — similar to what a patient gets in the hospital through an oxygen mask.