FOXI1 and neoplasm: In this study, we identified inter-tumour heterogeneity of sporadic ChRCCs, characterized by mutually exclusive expressions of L1CAM and FOXI1. FOXI1 is an important transcription factor for differentiation of intercalated cells of the collecting duct and, importantly, Notch signalling regulates differentiation of ureteric bud cells either into L1CAM-positive principal cells of the collecting duct when Notch signalling is active, or into FOXI1-positive intercalated cells of the collecting duct when Notch signalling is inactive.18