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Exercise, which has been proven to reduce bone loss, might also fight cancer, according to a new study.

The new study conducted at Cornell University found that making bones stronger seems to make tumors weaker, leading researchers to suggest that weight-bearing exercise might have anti-cancer effects.

Researchers experimented on both animal and in vitro models and found that that causing bone to bear moderate, repeated weight (similar to an exercise regimen) led to inhibited growth of bone tumors composed of metastasized breast cancer cells.  The findings suggest that such mechanical stimulation might reduce the expression of genes that interfere with normal, health bone functioning.

Researchers explain that breast cancer often metastasizes to bone.  Bones then deteriorate because the tumor disturbs the normal process of bone remodeling.  Afterwards, the bone loss, which is caused by too much bone breakdown, or osteolysis, helps promote the tumor because the bone is a depot of factors that promote tumor growth. Degraded bone releases these stored factors, and the tumor grows.

The findings revealed that mechanical stimulation of a mouse tibia injected with malignant breast cancer cells kept the tumor from growing and increased bone mass.  However, doing nothing allowed the tumor to proliferate and the bone to degrade.

"If you think about typical cancer treatment, like chemotherapies, they are targeting the cancer cells," first author Maureen Lynch said in a news release. "So we needed to figure out if loading is affecting the tumor cells in addition to the bone cells, or if this is some kind of indirect effect. We found a little bit of both."

After further analysis, researches found that while genes involved in cancer were largely unaffected by loading, one gene called Runx2, a transcription factor that regulates genes expression and production of other proteins, was significantly affected by mechanical loading.

Researchers explain that Runx2 might direct cancer cells to secrete proteins that stimulate osteolysis, which can lead to bone loss. However, researchers believe mechanical loading inhibits the expression of Runx2, which is why proteins that affect osteolysis are also reduced. 

While additional studies are needed to confirm the recent findings, researchers believe insights from the latest research could lead to drug therapies and targeted exercise regimens for cancer patients.

"Specifically, physically mediated mechanisms in bone might be contributing to bone loss in cancer patients," senior author Claudia Fischbach-Teschl said in a news release. "So harnessing those things better is what could really help patients."

The findings were published May 3 in the Journal of Bone and Mineral Research.