Malignant cells from various tumours invade the brain with help from an unlikely source: star-shaped cells that are themselves part of the brain.

Metastasis — the spread of cancer cells from their original site in the body to distant organs — causes 80% of cancer deaths. But few therapies target metastatic brain cancer, which can be seeded by cells from melanomas, breast tumours and other cancers.

Qing Chen at the Wistar Institute in Philadelphia, Pennsylvania, and her colleagues found that brain cells called astrocytes encourage the multiplication of cancer cells that have infiltrated the brain. The researchers demonstrated that astrocytes shunt the brain’s fatty acids to the invading cancer cells. The fat binds to a protein, PPAR-γ, within metastatic cells and triggers a molecular pathway that results in cell proliferation.

The researchers injected cancer-ridden mice with a compound that blocks PPAR-γ. After the injections, the animals’ brain tumors stopped growing — suggesting that PPAR-γ-blocking compounds could help to control brain metastasis. The role of PPAR-γ possibly depends on cancer type; as a result, therapies that target it might help some people with cancer more than others.