THY1 and cancer: To determine whether RCOR2 controls cancer cell plasticity leading to tumor initiation, we isolated aldehyde dehydrogenase–high (ALDHhi) breast cancer stem cells (BCSCs; Lin–CD90–ALDHhi) from PyMT mammary tumors by flow cytometry and found elevated RCOR2 protein in this cell population compared with Lin–CD90–ALDHlo non-BCSCs (Figure 3C).