A drug that targets the white blood cells fostering brain tumours — rather than the cancer cells themselves — shrinks tumours in mice.

The aggressive brain cancer known as glioblastoma is notoriously difficult to treat. Johanna Joyce at the Memorial Sloan-Kettering Cancer Center in New York and her colleagues gave mice with glioblastomas a drug that inhibits a cell-surface protein called colony-stimulating factor-1 receptor. This protein is expressed mainly on the white blood cells, or macrophages, that surround the tumour.

The 22 mice that did not receive the drug all died within 8 weeks. By contrast, 64% of the mice given the drug were still alive after 26 weeks. Surprisingly, the drug did not kill the macrophages but instead altered their gene expression, presumably turning off tumour-promoting functions.

Nature Med. 19, 1264–1272 (2013)