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. The gene discussed is PIK3CA; the disease is cancer.