A team of researchers based out of Harvard Medical School, the Dana Farber Cancer Institute, and the University of Vermont has found that stretching reduces tumor growth by 52 percent in mice injected with breast cancer cells. The team's study is published in the journal Scientific Reports.

Sixty-six female mice were injected with tumors then randomized to two groups. Mice in the first group received ten minutes of stretching once a day for four weeks, in which they were "held by the tail and gently lifted, allowing the front paws to grasp a bar" (see figure A below)." Mice in the second group were simply placed on a table for the ten minutes.

After four weeks, tumors in the stretched mice were half the size of those in control group mice on average (see figure B above), an impressive result. Examining the tumors and the surrounding cells after the study period, the researchers found signs of reduced inflammation and boosted immune cell activity in the stretched mice.

Northwestern University medical researcher Dr. Sam Weinberg expressed skepticism at the study's large effect size, but says the findings are definitely worth exploring further.

"I suspect that any micro injury may improve tumor clearance if the immune system gets active," he said.

Weinberg would love to see a follow-up study on a mouse model with non-injected breast tumors where the researchers observe if stretched mice actually live longer than unstretched controls. He expressed concern that stretching could actually cause the tumors to break up and spread, a worry that the researchers shared in their paper as well.

The researchers say their study is the first report of reduced cancer growth in response to stretching. Make no mistake, however, it does not indicate stretching as a primary treatment for cancer. Further research will be needed to verify the impressive early results and ascertain any negative side effects. After more successful animal trials, human studies could follow.

Resistance exercise has already been linked to a lower risk of death in cancer patients, so it's possible stretching could have similar benefits.

"The potential clinical significance of our results lies in the possibility of developing a method of gentle stretching that could be well tolerated and testable in humans for primary or secondary cancer prevention, or in conjunction with cancer treatment," the researchers write.

Source: L. Berrueta, J. Bergholz, D. Munoz, I. Muskaj, G. J. Badger, A. Shukla, H. J. Kim, J. J. Zhao & H. M. Langevin. Stretching Reduces Tumor Growth in a Mouse Breast Cancer Model. Scientific Reports volume 8, Article number: 7864 (2018) doi:10.1038/s41598-018-26198-7