Whereas a moderate ARID1A protein expression was observed in normal urothelial samples (median Remmele Score: 6), ARID1A protein levels were increased in all carcinoma subgroups, with strongest expression in high-grade papillary tumors, namely pTa high-grade (median Remmele score: 12, P < 0.001), CIS (median Remmele score: 12, P < 0.001) and pT1 high-grade cases (median Remmele score: 12, P < 0.05) (Fig 3A–3G). Here, ARID1A is linked to in situ carcinoma.