Exercise may do more than keep the body fit during cancer treatment. A new study suggests that physical activity can change the immune system inside the lungs and may help remove some of the disadvantages linked to obesity.
Researchers at Roswell Park Comprehensive Cancer Center discovered that obesity was associated with an immune environment that was less effective at fighting lung tumors. When obese laboratory mice exercised, some of those immune changes shifted in a healthier direction and their tumors grew more slowly.
The findings were published in the Annals of Surgery. The research was led by a team including Dr. Sai Yendamuri and Andrew Ray of Roswell Park Comprehensive Cancer Center.
The study focused on non-small cell lung cancer, the most common form of lung cancer. This broad group includes several types of tumors and represents roughly eight out of every 10 lung cancer cases.
Doctors now understand that cancer is not made up only of tumor cells. A tumor lives inside a complicated neighborhood containing blood vessels, normal tissue and many types of immune cells.
Some immune cells attack cancer, while others can unintentionally protect it. The balance between these opposing forces can influence whether a tumor continues growing and may also affect how well treatments work.
Obesity can disturb that balance. Fat tissue produces hormones and chemical signals that can alter inflammation and immune function, which may help explain why excess body fat has been connected with the risk or outcome of several cancers.
The researchers asked a simple question: could exercise push the immune system back toward a state that is better able to attack lung tumors? To investigate, they studied lean and obese mice under several different conditions.
Some mice were healthy and others had non-small cell lung cancer. Within each group, some animals had access to a running wheel while others did not exercise.
The scientists examined immune cells from the lungs and tumors. They also studied patterns of gene activity to understand how exercise changed what was happening at a biological level.
A major difference involved regulatory T cells. These cells help keep the immune system under control so it does not attack healthy tissue, but cancer can take advantage of them because they can also weaken the immune response against tumors.
Obese mice that exercised had fewer of these suppressive cells than obese mice that remained inactive. At the same time, exercise increased the presence of CD8 T cells, which are immune cells capable of killing cancer cells.
That combination could be important. Reducing cells that hold back an immune attack while increasing cells that can destroy tumors may create conditions that make it harder for cancer to grow.
This is what the researchers observed in the animals with lung cancer. Tumors grew more slowly in the mice that exercised, providing evidence that physical activity was linked not only with different immune-cell numbers but also with changes in the cancer itself.
The scientists then examined whether the animal findings were reflected in people. They analyzed lung cell samples from 73 patients who had non-small cell lung cancer.
Patients were grouped according to their amount of body fat and their level of physical activity. Those who exercised had fewer regulatory T cells and fewer fat-enhanced myeloid cells in their samples.
Myeloid cells normally have many important jobs in the immune system, including responding to infection and damaged tissue. In cancer, however, certain forms of these cells can suppress tumor-killing immune responses and create conditions that help cancer survive.
The human results therefore pointed in the same general direction as the mouse experiments. Physical activity was associated with fewer immune cells that can weaken the body’s attack on cancer.
This does not yet mean that doctors can prescribe exercise as a treatment for lung cancer. The study showed that exercise was associated with potentially helpful immune changes, but it did not prove that exercising patients survive longer or respond better to cancer therapy.
There are also differences between controlled experiments in mice and the complicated reality of human cancer. In the patient analysis, people chose their own activity levels, so other health and lifestyle differences could partly explain the results.
Another question is how much exercise is needed. The study does not establish a single exercise program, intensity or duration that will produce the best immune response in every patient.
Even with these limitations, the research adds to growing interest in exercise as supportive cancer care. Physical activity can already help some patients maintain strength, mobility and quality of life, and this study suggests there may also be effects on the immune system surrounding a tumor.
Senior author Andrew Ray described exercise as a free and noninvasive addition that could potentially support standard treatment. It should be viewed as an addition, not a substitute for proven cancer therapies.
Future clinical trials will need to test structured exercise programs in larger groups of lung cancer patients. Researchers will need to determine whether the immune changes seen here translate into slower disease progression, stronger responses to immunotherapy or other treatments, and ultimately longer survival.
The study’s most interesting message is that the body’s cancer-fighting environment may not be fixed. If human trials confirm the results, something as familiar as regular physical activity could become one more tool for helping the immune system work against lung cancer.
If you care about cancer, please read studies that artificial sweeteners are linked to higher cancer risk, and how drinking milk affects risks of heart disease and cancer.
For more health information, please see recent studies about the best time to take vitamins to prevent heart disease, and results showing vitamin D supplements strongly reduces cancer death.
Source: Roswell Park Comprehensive Cancer Center.
