University of California Berkeley scientists have discovered a protein that determines if breast cancer will spread and become deadly.

The protein–SATB1–changes the levels at which more than a thousand genes are expressed in breast cancer cells, seemingly controlling whether cancer cells will survive elsewhere.

The scientists say the protein–found inside the nuclei of cells–would be difficult and potentially dangerous to target with drugs. However, SATB1 levels could be used as a prognostic test.