WASHINGTON — A provocative study in mice suggests something as simple as breathing in extra oxygen might give immune cells a boost in attacking cancer. The immune system often can spot and destroy abnormal cells before they grow into cancer. But when tumors manage to take root, they put up defenses to block new immune attacks. With the extra oxygen, “you remove the brake pedal” that cancer can put on tumor-fighting immune cells, said Michail Sitkovsky, director of the New England Inflammation and Tissue Protection Institute at Northeastern University, who led the work.

Tumors can grow so rapidly that they outpace their blood supply, creating a low-oxygen environment. The lack of oxygen in turn spurs cancer cells to produce a molecule called adenosine, which essentially puts nearby tumor fighters called T cells and natural killer cells to sleep, explained pharmacologist Edwin Jackson of the University of Pittsburgh, study co-author.

Sitkovsky’s team wondered if just getting more oxygen to an oxygen-starved tumor could strip away that defense.

They put mice with different kinds of lung tumors inside chambers that mimic supplemental oxygen therapy. The extra oxygen changed the tumor’s environment so that immune cells could get inside and do their jobs, the researchers reported in the journal Science Translational Medicine.