When hypoxic and aggressive tumors were treated with an “oxygen challenge,” tumor growth was delayed in an irradiated animal model. Measuring the oxygenation of tumors can be a valuable tool in guiding radiation therapy, which opens the door for personalized therapies that keep tumors in check with oxygen enhancement.

This study, published in Magnetic Resonance in Medicine (2013; doi: 10.1002/mrm.24846), found that smaller tumors, as determined by magnetic resonance imaging, were significantly better oxygenated than larger ones. This confirmed previous investigations that show a range of hypoxic environments depending on the size of the tumor.

“The next step is clinical trials to assess tumor response to radiation therapy,” said Ralph Mason, PhD, director of the cancer imaging program at the University of Texas Medical Center in Dallas. “Tumors determined to be hypoxic can be evaluated and made responsive through mild and easy-to-administer interventions, such as breathing more oxygen or taking a vasoactive drug. Monitoring the response to oxygen breathing tells us which tumors will benefit.”

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If the results are confirmed in humans, the implications for personalized therapies for other cancers could mean fewer radiation treatments, or perhaps, ideally, one single high-dose treatment. Lung cancer, for instance, is a form of the disease whose tumors are poorly oxygenated despite being located in the principle organ charged with oxygenating the blood.

“The ability to stratify tumors based on hypoxia offers new opportunities to tailor therapy to tumor characteristics, potentially enhancing success through personalized medicine,” Mason said. He is collaborating with colleagues to start clinical trials to assess the effectiveness of oxygenation during treatment with stereotactic body radiation in humans.

Mason’s research team has worked to understand how low oxygen concentration can cause radiation resistance in tumors. In some cases, the simple addition of oxygen to stereotactic body radiation greatly improves response. The key is to identify which patients will benefit.