PIWIL2 and cervical cancer: Sphere-forming cells derived from cervical cancer expressed PIWIL2 and stem cell-related genes such as POU5F1, c-MYC, STAT3, SOX2 and exhibited stem cell properties, such as tumor formation, absence of CD34 and CD105 and expression of CD44, a marker of CSCs, and ABCG2, which conferred them resistance to doxorubicin [90].