A protein that promotes the metastasis to the brain of breast, lung and other cancers has been identified.

When cancer cells break off from their initial tumour they can spread throughout the body and invade other organs to form new tumours, in a process known as metastasis. Although metastatic tumours cause 90% of deaths in cancer patients, the underlying mechanisms are not well understood.

A protein, known as CEMIP, has been found to promote metastasis to the brain. Brain metastasis is one of the deadliest types of metastasis, as it is extremely challenging to treat. Brain tumours are difficult to operate on, due to the risk of brain damage, and many chemotherapy drugs are unable to pass through the blood brain barrier.

CEMIP was found in high levels in metastatic breast and lung cancer cells. The protein was released from the metastatic cells in exosomes, the extracellular vesicles that cells secrete as chemical messengers. It was discovered that the CEMIP containing exosomes were taken up by both the blood and immune cells of the brain. Once inside the cells, CEMIP is able to trigger the production of inflammatory molecules that have been linked to metastasis.

Breast cancer cells that were prevented from producing CEMIP were unable to colonise brain cells in both tissue and animal models. However, providing CEMIP filled exosomes to the cells restored their metastatic ability.

Primary tumour samples from patients with metastatic brain cancer were found to have higher levels of CEMIP compared to patients with other types of metastatic tumour. Higher CEMIP production in the primary tumour was also linked to the time it took for the cancer to metastasise, suggesting that CEMIP could be a useful biomarker for estimating brain metastasis risk.

The researchers are now working on both a diagnostic test to detect CEMIP levels, and an antibody that could potentially delay brain metastasis by blocking CEMIP release.

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