ERBB3 and neoplasm: To evaluate HPK bioparticles against molecules that engage more traditional routes of BBB passage for targeting intracerebral tumours, we first compared human gene expression of HER3 (ErbB3) against conventional BBB transporters, transferrin receptor (TfR, encoded by the TFCR gene) and glucose transporter (GLUT1, encoded by the SLC2A1 gene).