Protein May Slow or Stop Tumor Cell Metastasis

The secretion of a particular protein by tumor cells may be the key in preventing tumors from metastasizing, new research has discovered.

Tumors that secrete the protein prosaposin do not spread, researchers at Children’s Hospital Boston found. Lead researcher, Dr. Randoph S. Watnick, assistant professor, Vascular Biology Program, and colleagues previously discovered that metastatic tumors did not simply start spreading to other organs—they prepared the next site of metastasis “by secreting proteins that encourage tumor cells to grow in the new site by doing things like attracting feeder blood vessels.” This new discovery has identified a specific protein that plays a role in the process. Prosaposin was found to inhibit the preparation of the next site for tumor growth by “producing compounds that block the growth of blood vessels.” When tumors secreted this protein, they did not metastasize.

Watnick and fellow researchers examined localized breast and prostate tumors and discovered that they were secreting “very high” levels of prosaposin, while metastasized tumors were secreting limited amounts of the protein. The next step of the research involved injecting mice with tumor cells that they knew, from previous research, would spread, but injected the cells with prosaposin. This step revealed that lung tumors that had developed as a result of metastasis were reduced by 80%, metastases in the lymph nodes were destroyed entirely, and the life span of the mice increased by 30% when they were given prosaposin.

If the same therapeutic effect can be replicated in humans, Watnick said, cancer patients may one day be treated for a primary tumor and, at the same time, given medication to slow or stop the chance of metastasis.

"While we may not be able to keep patients from getting cancer, we can potentially keep them metastasis-free," Watnick added.

Additional information was gathered from the charity Cancer Research UK.