This is an interesting in vitro study of the effect of exercise on inhibiting growth of cancer cells: Exercise-induced muscle-derived cytokines inhibit mammary cancer cell growth
Regular physical activity protects against the development of breast and colon cancer, since it reduces the risk of developing these by 25–30%. During exercise, humoral factors are released from the working muscles for endocrinal signaling to other organs. We hypothesized that these myokines mediate some of the inhibitory effects of exercise on mammary cancer cell proliferation. Serum and muscles were collected from mice after an exercise bout. Incubation with exercise-conditioned serum inhibited MCF-7 cell proliferation by 52% and increased caspase activity by 54%. A similar increase in caspase activity was found after incubation of MCF-7 cells with conditioned media from electrically stimulated myotubes. PCR array analysis (CAPM-0838E; SABiosciences) revealed that seven genes were upregulated in the muscles after exercise, and of these oncostatin M (OSM) proved to inhibit MCF-7 proliferation by 42%, increase caspase activity by 46%, and induce apoptosis. Blocking OSM signaling with anti-OSM antibodies reduced the induction of caspase activity by 51%. To verify that OSM was a myokine, we showed that it was significantly upregulated in serum and in three muscles, tibialis cranialis, gastronemius, and soleus, after an exercise bout. In contrast, OSM expression remained unchanged in subcutaneous and visceral adipose tissue, liver, and spleen (mononuclear cells). We conclude that postexercise serum inhibits mammary cancer cell proliferation and induces apoptosis of these cells. We suggest that one or more myokines secreted from working muscles may be mediating this effect and that OSM is a possible candidate. These findings emphasize that role of physical activity in cancer treatment, showing a direct link between exercise-induced humoral factors and decreased tumor cell growth.
Study shows that a humoral factor is involved, that is, a chemical – a cytokine – released into general circulation by skeletal muscle. To me this also suggests that weightlifting / bodybuilding may be the most effective form of exercise for preventing or stopping cancer, since more weightlifting leads to more muscle, and the muscle will secrete more of the cytokine responsible. That would depend, however, on the best way to produce the cytokine, for instance higher intensity vs greater volume of exercise. But just the fact that weightlifting involves virtually all the muscles in the body suggests that it will be better than endurance exercise for the purpose of preventing cancer.