Although previous immunohistochemistry studies have shown aberrant expression of claudin-1, -3, -4, and -7 proteins in human tissues of UTUC [26] and bladder cancers [38], the expression of claudin-5 and its regulatory role in TJ homeostasis during UTUC tumorigenesis still remains elusive. Here, CLDN1 is linked to renal pelvis/ureter urothelial carcinoma.