ERBB2 and cancer: Neurons and glial cells work together to construct the PMN of the brain, and their interactions with cancer cells are crucial for promoting brain metastasis.228 Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter that plays a critical role in the central nervous system.229 In the clinical analysis of HER2+ and TNBC brain metastasis, cancer cells have been observed to overexpress GABA-related proteins (such as GABAA receptors, GABA transporters, GABA transaminases, and glutamate decarboxylase).