LIF and neoplasm: To identify a potential serum factor responsible for inducing the tumor-like growth in mESCs, initially we focused on molecules known to sustain the self-renewing growth of mESCs, such as LIF [9], [10], Bmp4 [14], vitamin A derivatives (all-trans retinoic acid, RA [15], and retinol [16], [17]), and simultaneous inhibition of Erk and Gsk3β [31].