EC subtypes involve mutations in AT-Rich Interaction Domain 1A (ARID1A), Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PI3KCA), Phosphatase And Tensin Homolog (PTEN), Protein Phosphatase 2 Scaffold Subunit Alpha (PPP2R1α), and mismatch repair deficiency; OCCC subtype comprises de novo expression of HNF1β [24,25] and ARID1A, PI3KCA, PTEN, Catenin Beta 1 (CTNNB1) and PPP2R1α mutations; MC comprises tumours with mutations in KRAS and high frequency of ERBB2 amplification with overexpression of mucin-coding genes [26,27]. The gene discussed is ARID1A; the disease is neoplasm.