BioEd Online

A deadly childhood brain cancer has long been thought to spread through fluid in the brain. But new findings show that the tumour cells can travel through the blood.

Medulloblastoma, which forms at the base of the skull, is the most common type of malignant brain tumour in children. When it spreads, or metastasizes, it is nearly always to the leptomeninges — inner membranes that envelop the brain and spinal cord. Scientists had assumed that medulloblastoma cells migrate there through the cerebrospinal fluid, the clear liquid that bathes the leptomeninges and cushions the brain.

But Michael Taylor of the Hospital for Sick Children, in Toronto, Canada, and his colleagues found tumour-specific DNA in patients’ bloodstreams. The team also found tumour cells circulating in the blood of three separate individuals. When the researchers grafted tumours into mice on the animals’ flanks, far from the cerebrospinal fluid, the mice developed metastases in the leptomeninges, confirming that the cancer can spread through the blood.