Certain cancers, such as triple-negative breast cancer, produce antibodies that, although they help fight the tumor, can cross the blood-brain barrier and alter the function of NMDA receptors (NMDAR) in the brain, which are essential for neuronal signaling. Scientists at Cold Spring Harbor Laboratory (CSHL) have identified their origin and described how this process is linked to the maturation of these antibodies, which can activate or inhibit the receptor, causing neurological and psychiatric symptoms.