Exercise Aid Cancer Treatment

In a new study involving mice, aerobic exercise slowed the growth of breast cancer tumors and made the cancer more sensitive to chemotherapy. The results raise the possibility that exercise may change the biology of some malignant tumors, potentially making them easier to treat.

Scientists and clinicians have known for some time that solid tumors can create their own, peculiar ecosystem within the body. As a tumor grows, it sends out biochemical signals that prompt the creation of additional blood vessels to provide the expanding tumor with more oxygen. Oxygen is, of course, important for cell health, including in normal tissue.

But in some tumors, these new blood vessels begin to proliferate so wildly that they create a “jumble and tumble” of tubes that can curl around and choke one another, reducing blood supply and oxygen to the tumor, says Dr. Mark W. Dewhirst, the Gustavo S. Montana Professor of Radiation Oncology at Duke University School of Medicine in Durham, North Carolina, and senior author of the new study.

As a result, the tumor becomes hypoxic; it exists in an environment with little oxygen.

That condition might seem desirable, since it is fundamentally unhealthy for living tissue to be starved of oxygen. But unfortunately, Dewhirst says, hypoxia also can make tumors relatively impervious to treatment. Chemotherapy drugs and radiation work better in conjunction with oxygen.

“It’s a bad sign from a clinical perspective when a tumor is hypoxic,” Dewhirst says.

For years, he and his colleagues have been looking for ways to increase oxygen flow to tumors.

There have been trials in animals and people of substances that alter the biochemical signals from the tumors and lead to slower, more normal blood vessel growth to the tumor and reduced hypoxia. But the benefits of this approach have so far been fleeting; eventually the blood vessels leading to the tumor tend to overgrow again like untended vines and hypoxia returns.