PARP1 and cholangiocarcinoma: Some new substrates of USP1 have also been found in several tumors, such as karyopherin subunit alpha 2 and ERa in breast cancer [15,24], ID2 in gastric cancer [22], c-kit and TBLR1 in liver cancer [23,27], TAZ in osteosarcoma and hepatocellular carcinoma [23,28], Snail in ovarian cancer [18], and PARP1 in cholangiocarcinoma [29].