The researchers found manipulating levels of nitric oxide, or NO, might improve the disorganized network of blood vessels supplying tumors, potentially improving the effectiveness of radiation and chemotherapy.

The scientists at Massachusetts General Hospital's Steele Laboratory of Radiation Oncology conducted an experiment in which NO production was selectively suppressed in tumor cells while being maintained in blood vessels. The result was a significant improvement in the appearance and function of the tumor's blood supply.

"Our finding suggests that the creation of perivascular NO gradients -- differences between the levels produced in blood vessels and those found in tumor tissue -- may be able to normalize tumor vasculature," said Dr. Dai Fukumura, who led the study. "Combining the use of angiogenesis inhibitors, which normalize vasculature through a different mechanism, with the blockade of nonvascular NO production, may produce even greater improvement in therapeutic outcomes."

The study is to appear in the journal Nature Medicine.