NECTIN4 and cancer: Nectin4 is ubiquitously expressed in human embryonic cells but hardly in normal adult tissues, while it is highly expressed on the surface of malignant solid tumors such as urothelial cancer, ovarian cancer, and melanoma, playing key roles in various aspects of tumor progression like proliferation, angiogenesis, epithelial-to-mesenchymal transition, metastasis, DNA repair, tumor relapse, and poor prognosis of these epithelial malignancies (10–13).