Microsatellite stable AH have fewer cancer-driving mutations than EEC, and 79% of microsatellite stable EEC gain cancer driver mutations related to PTEN, CTNNB1, ARID1A, CHD4, and PIK3CA, indicating that some AH lesions are immediate precursors of EEC, and their progression depends on the acquisition of additional cancer driver mutations. The gene discussed is ARID1A; the disease is cancer.