Breast Cancer Metastasis
Metastasis, where cancer cells break off from the primary tumour and form a new tumour elsewhere in the body, is particularly deadly for breast cancer patients. Breast cancer is prone to metastasising in the brain, which is challenging to treat. However, new research that demonstrates breast cancer cells can use exosomes to metastasize the brain could provide an intriguing new treatment avenue.

Exosomes and Cancer
Exosomes are extracellular vesicles released by cells, often containing chemical signalling molecules. Cancer cell can release chemical signals in exosomes are to create a more hospitable environment for the tumours. For example, some exosomes can degrade the cytoskeleton that supports normal body cells, which allows the tumour more room to grow. Exosomes are also key to promoting metastasis and can be released from the primary tumour to start the growth of a second tumour elsewhere in the body. However, until recently it was not understood how exosomes could be used to metastasize in the brain.

Hijacking the Blood Brain Barrier
The blood brain barrier separates the circulatory system from the extracellular fluid surrounding the brain and spinal cord. It is an extremely selective barrier which usually only allows small molecules through. As exosomes are 2000 times larger than the size limit for passive transport through the blood brain barrier researchers had previously wondered if exosomes could squeeze into the gaps between the tightly packed endothelial cells to pass through. However, the study showed that exosomes trick the endothelial cells into taking them up and releasing them on the other side of the barrier. Once the exosomes have passed through the barrier, they can also hijack the resident brain cells, astrocytes, to release signals promoting a hospitable tumour environment. The researchers demonstrated that these signals can degrade the cell cytoskeleton.

Future Therapies
It is extremely difficult to deliver drugs to the brain as many cannot pass through the blood brain barrier. Therefore, the researchers now want to utilise the exomes to deliver drugs though the blood brain barrier. The discovery also gives avenues for preventing breast cancer metastasis by stopping the transport of exosomes across the barrier.

At the World Metastasis Summit, taking place in Boston this November, Kin-Hoe Chow from Dana-Farber Cancer Institute will be discussing Patient Derived Models of Metastatic Brain Tumors: A Resource for In Vivo and Ex Vivo Research, you can view the full agenda here.