PIK3R1 and esophageal squamous cell carcinoma: Other genes with a higher AUC (over 0.9) for distinguishing ESCC were PIK3R1 and CDKN2A. PIK3R1 encodes a p85 regulatory subunit alpha and appears to play a tumor suppressor role because PI3K subunit p85α (p85α) regulates and stabilizes p110α [28].