Scientists identify inhibitor of tumour spread

In collaboration with the Press Association

US scientists have found evidence that tumours that do not spread to other parts of the body secrete a particular protein - a discovery that may be harnessed in the future and used to prevent cancers from spreading.

Metastasis, or cancer spread, is one of the main causes of death from cancer, so scientists worldwide have been searching for a way to block it.

Cancer researchers recently discovered that some tumours release proteins that travel through the blood to distant organs, where they prepare the site for cancer cells to form new tumours.

Now, scientists at Children's Hospital Boston have shown that tumours that do not spread secrete a protein called prosaposin. This appears to encourage the production of other proteins that block this process and so prevents metastasis.

Large amounts of prosaposin were found to be secreted by prostate and breast tumours that did not spread, while metastatic tumours were shown to secrete very little of the protein.

To test the effect of prosaposin, the researchers injected mice with highly metastatic tumour cells as well as the protein.

They found that the addition of prosaposin brought about an 80 per cent reduction in new cancers forming in the lung and completely blocked them from developing in the lymph glands.

Survival time was also greatly increased, with mice living at least 30 per cent longer than those which had not received prosaposin.

The scientists also discovered that prosaposin works by switching on a 'tumour suppressor' gene called p53 in the tissue surrounding the tumour, which in turn stimulates an inhibitor of blood vessel growth called thrombospondin-1.

Their findings are published in the Proceedings of the National Academy of Sciences and, if they are confirmed in larger studies, could pave the way for a new therapy to prevent or slow down the spread of cancer.

Dr Randoph Watnick, assistant professor in the Vascular Biology Programme at Children's Hospital Boston, commented: "Prosaposin, or derivatives that stimulate p53 activity in a similar manner in the tumour stroma, might be an effective way to inhibit the metastatic process in humans.

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

Dr Julie Sharp, Cancer Research UK's senior science information manager, said: "Stopping cancer spread is a huge challenge in the treatment of cancer patients. This study has revealed crucial differences between cancers that spread and those that don't, revealing that some tumours actually send out messages to prevent spread.

"While this research is in its early stages it could help researchers to develop drugs that stop or slow down cancer spread."