GAD1 and breast carcinoma: Interestingly, perhaps as an adaptability mechanism, metastatic breast cancer cells invading the brain express GABAA-R and a repertoire of related proteins similar to those of GABAergic neurons, including GABA transaminase (GABAT), glutamate decarboxylase (GAD67), GABA transporter, reelin, and parvalbumin.279 The 15 isoforms of the GABA receptor mRNA, as well as vesicular GABA transporter (VGAT), GABA 1 to 3 transporter (GAT1-3) and the betaine-GABA transporter (BGT) expression are highly regulated in HER2+ breast cancer brain metastases.