In this study, we evaluated SOX2, OCT4, or NANOG in ovarian TICs, and used in vitro and in vivo studies to determine that SOX2, relative to OCT4 or NANOG, more strongly correlates with 3-D spheroid growth, tumor-initiating capacity, and chemoresistance in ovarian cancer cells, regardless of histology. Here, NANOG is linked to neoplasm.