ABCG2 and retinoblastoma: Previously, we reported that ATP binding cassette protein G2 (ABCG2) and mini chromosome maintenance protein 2 (MCM2) cancer stem cell (CSC)-like markers are expressed in retinoblastoma tumors [9], and recent reports have demonstrated that stem cells expressing Oct4, Nanog, ALDH1, and low Hoechst 33342 cells are present in human RB cells [10,11].