ARID1A and papillary carcinoma: Interestingly, ARID1A alterations are present in both subgroups of MIBC, i.e. in cases potentially arising from high-grade papillary carcinomas (pTa HG) (35/133 = 26%) and tumors of non-papillary origin developing from carcinoma in situ (67/269 = 25%) (Fig 1A).