NECTIN4 and cancer: Nectin-4, also known as PVRL4 (poliovirus-receptor-like 4), is specifically expressed in the embryo and placenta, recent studies have reported that it is also over-expressed in several human cancers, including lung, gastric, ovarian and breast cancers, and the expression level of Nectin-4 in cancer tissues is significantly associated with cancer progression and poor prognosis of the patients [7–13].