PHILADELPHIA -- In a discovery that might help explain why widely used cancer therapies are less than optimal, Duke University Medical Center researchers have found that a tumor's oxygen level and blood flow can fluctuate rapidly. The Duke animal study, which contradicts previous assumptions about tumors, could be important because the two major cancer treatments, radiation and chemotherapy, depend on a constant high oxygen level and steady blood flow within a tumor, scientists said. "These fluctuations in oxygen level and blood flow are not predictable and might represent an impediment to radiation therapy and drug therapy," said Mark Dewhirst, co-director of the radiation oncology and hyperthermia program at Duke Comprehensive Cancer Center and associate professor of pathology. "Before this work, there was no way to reliably measure these values."
Dewhirst prepared the findings for presentation Tuesday at an American Association for Cancer Research meeting. His study, which was done in collaboration with Rod Braun, assistant professor in radiation oncology, was funded by the National Cancer Institute. A report based on the results of this study has been accepted for publication by the American Journal of Physiology. High oxygen levels are crucial for effective radiation therapy, Dewhirst explained, because radiation kills tumor cells by forming oxygen radicals -- highly reactive oxygen atoms that damage DNA.
Chemotherapy might be affected by the fluctuations, Dewhirst said, because if tumor blood flow drops, the drugs might not be delivered efficiently throughout the tumor.
While low oxygen levels, called hypoxia, are known to exist in certain tumors, researchers had not measured changes in oxygen levels over time. In the current study, Dewhirst and his colleagues measured oxygen levels in mammary tumors in seven rats using an electrochemical probe that produces an electrical current depending on the amount of oxygen present in the tissue.