It has long been known that cancer metastasis is not determined solely by blood volume or lymphatic flow but that there is a biological predilection for spread to particular organs. The underlying mechanisms that contribute to this organotropism remain elusive. Brain metastases are an increasingly common site of treatment failure for breast cancer patients and present a leading edge for future clinical gains. Borrowing from investigations in glioma and stroke, the formidable blood-brain barrier (BBB) is known to become penetrable as a result of neoplastic invasion and is occasionally referred to as the blood-tumor barrier. However, for circulating tumor cells, the BBB encountered during attempts to intravasate into the neural niche is intact and formidable. So how does a circulating breast tumor cell breach the BBB? A recent publication that focused on liver and lung metastases provided some provocative insights into the mechanisms of organotropism germane to neurosurgeons and neuroscientists.
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