Exercise shown to reduce numbers of circulating tumor cells in patients with colon cancer

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Could exercise prevent certain types of cancer from recurring, by not only prompting a healthy lifestyle, but by altering the biological mechanisms of cancer cells?

That is what Dana-Farber Cancer Institute scientists believe may be occurring, according to a pilot study that showed exercise was associated with a reduction of circulating tumor cells (CTCs) in the bloodstream among a small group of patients following treatment for colon cancer.

The benefits of exercise for patients with colon and other forms of cancer has been previously recognized in retrospective, observational studies. However, the exact mechanisms by which exercise helps keep cancer at bay remain uncertain. In new research published today in the journal Public Library of Science (PLOS), investigators report that exercise may reduce the amount of circulating tumor cells (CTCs) in the body, therefore potentially reducing the risk of disease recurrence.

“While this study is small in scale, we believe it is the first to demonstrate that exercise reduced circulating tumor cells in patients with colon cancer,” said the paper’s first author, Justin Brown, PhD, a researcher in Dana-Farber Cancer Institute’s Division of Population Sciences. “The results shed new light on mechanisms through which exercise may improve disease outcomes among patients with colon cancer and should lead to further investigation of exercise as means to help reduce cancer recurrence risk.”

Cancer metastases have long been thought to be spurred by cells that break away from the primary tumor and travel in the blood stream to distant parts of the body. Just one of these circulating tumor cells remaining in the body following surgery and chemotherapy in stage III colon cancer patients can result in a six-fold risk increase of the disease returning.

To test whether exercise affected the presence of CTC’s in the bloodstream, the study enrolled 23 patients with stage I-III colon cancer, who had completed surgical resection and adjuvant chemotherapy. The patients were randomized to one of three groups; a moderate 150 minute per week exercise group, a higher intensity 300 minute per week exercise group, or non-exercise control group. A blood sample was taken from each participating patient to establish a CTC baseline using a novel technology called geometrically enhanced differential immunocapture (GEDI) platform, developed at the University of Pennsylvania.  

After a six-month period, blood samples were again taken from all three groups. The researchers found that in both exercise groups the number of CTCs in the blood stream had been significantly reduced, whereas no significant change in CTCs was observed in the control group.

Because both the moderate and high intensity exercise groups reduced the number of CTCs by roughly the same amount, the researchers postulate that these results may point to a direct biological or mechanical mechanism through which exercise reduces recurrence in colon cancer patients.

Exercise may also have an indirect effect on CTCs, according to Brown and colleagues. Of note, the exercise groups saw reductions in Body Mass Index (BMI), insulin levels, and sICAM-1, a protein associated with obesity. All three factors are associated with survival and recurrence in colon cancer patients in prospective cohort studies. These decreases led investigators to speculate that exercise may deprive the host tumor microenvironment of available growth factors, resulting in lower CTC counts.

“While additional research is needed to replicate our hypothesis-generating findings and to provide clinical context to these data, we believe these results represent a highly useful starting point to begin unraveling the biologic or biobehavioral mechanisms by which exercise may reduce disease recurrence in patients with colon cancer,” said Brown.

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