ABCG2 and head and neck squamous cell carcinoma: In this study, we further examined the expression of CSC properties, including the expression of other CSC representative markers, sphere-forming abilities, radioresistance and chemoresistance, drug-resistant genes (ABCG2 and MDR-1), and antiapoptotic proteins in the IL-33-overexpressing stable clones and HNSCC cells exposed to recombinant IL-33.