With 68% involving CG dinucleotides, C to T transitions are the most common mutation (51%) across all gastric cancers, while ARID1A mutations in GC usually contain indels relating to short C or G mononucleotide repeats, implying their occurrence by mismatch defect-induced microsatellite instability (49). The gene discussed is ARID1A; the disease is gastric cancer.