PIK3CA and neoplasm: Pathway analysis performed on the 2542 differentially expressed genes from the tumours and the 637 genes from GSC cultures identified 10 significant overlapping pathways, many of which have previously been related to TMZ resistance including; (i) DNA repair, (ii) G2M check point, (iii) E2F targets (iv) PI3K/Akt/mTOR signalling and (v) myc targets (Fig. 5c, Supplementary file 1).