Single exercise session raises anti-cancer myokines, lab tests show

A single 45-minute exercise session — either resistance training or high-intensity interval training (HIIT) — raised levels of muscle-derived proteins called myokines in women treated for breast cancer and was associated with reduced growth of breast cancer cells in laboratory tests, researchers reported.

The study, published this summer in Breast Cancer Research and Treatment, enrolled 32 women who had completed treatment for stage I to III breast cancer at least four months earlier. Blood samples taken before exercise, immediately after and 30 minutes after showed increases in several myokines; the researchers estimated the surge could slow cancer cell growth by roughly 20 to 30 percent in vitro.

Participants were assigned to one of two exercise protocols and completed about 45 minutes of activity in a single session. The resistance group performed eight repetitions for five sets across major muscle groups — including chest press, seated row, shoulder press, lateral pulldown, leg press, leg extension, leg curl and lunges — with one to two minutes of rest between sets. The HIIT group completed seven 30-second all-out bouts on machines such as a stationary bike, treadmill, rower or cross-trainer with three-minute rest intervals.

The largest immediate change was in the myokine interleukin-6 (IL-6), which rose by as much as 47 percent in the HIIT group. The resistance group showed a 23 percent increase in decorin, a myokine involved in tissue growth regulation, and a nine percent increase in IL-6. Myokine levels declined over time after exercise but remained above baseline at the 30-minute mark.

Francesco Bettariga, a PhD student at Edith Cowan University and the study’s lead researcher, said the findings provide a possible cellular-level explanation for prior epidemiological evidence linking regular exercise with reduced cancer progression, recurrence and mortality. He and colleagues cautioned that their laboratory measures do not prove long-term clinical benefit and said further in vivo work is needed.

In laboratory assays, researchers exposed breast cancer cells to blood serum collected from participants after exercise and observed reductions in cancer cell proliferation of up to about 30 percent compared with baseline serum. Those estimates are based on in vitro experiments and the authors noted that translating such effects to human patients requires additional study.

Myokines are proteins released by skeletal muscle during exercise that help muscles communicate with other tissues and organs. Prior research indicates some myokines can modulate metabolism, influence immune function and suppress inflammatory cytokines. Chronic inflammation and elevated pro-inflammatory cytokines have been linked to DNA damage and cancer development, a mechanism the authors cite as plausibly linking exercise to lower cancer risk.

The trial population had a mean age of 59 and an average body mass index of 28. The largest subgroup of participants had stage II disease (41 percent). The authors identified several limitations, including the small sample size, the focus on a single cancer type and the short-term nature of the intervention. They said future research will examine other cancers, different patient groups and the effects of regular, long-term exercise programs, as well as the role of the immune system in mediating anti-cancer responses.

Breast cancer is among the most common cancers in women. The American Cancer Society estimates about 311,000 new breast cancer cases are diagnosed in women in the United States each year and roughly 42,000 deaths occur annually. A separate analysis published in JAMA found breast cancer incidence rose about 0.8 percent per year from 2000 to 2019, a trend investigators have linked to factors including earlier onset of menstruation and exposure to hormone-disrupting chemicals.

Medical experts have long recommended regular physical activity to reduce the risk of obesity, cardiovascular disease and several cancers and to improve survival odds after a cancer diagnosis. The current study adds laboratory evidence that acute exercise triggers biological changes that can inhibit cancer cell growth in vitro, but the investigators and outside experts emphasize that clinical recommendations should await larger, longer-term trials that assess patient outcomes rather than surrogate laboratory measures.