ERBB2 and cancer: RAC2 also showed upregulation of proliferative pathways, including signalling by NTRK2/TRKB, characterised by overexpression of the PIK3CA gene, and signalling by ERBB2 in cancer, as reflected by elevated serum concentrations of SHC1, ERBB4, EGFR and ERBB2, compared with RAC3.