MKI67 and neoplasm: After co-culturing in serum-reduced medium for 4 days (medium was changed once after 48 h), tumor clones in the lower base wells were counted and examined by Ki67 immunostaining and proliferating cell nuclear antigen (PNCA) Western blot, and co-cultured pECs or control cells in the upper wells were stained by Hematoxylin.