Head and neck cancer stem cells: The side population

OBJECTIVES/HYPOTHESIS: The cancer stem cell (CSC) theory concludes that a subpopulation of cancer cells, the cancer stem cells, can self-renew and are responsible for tumor growth. Previous studies have identified cells able to efflux Hoechst 33342 dye as the side population (SP). SP cells and CSCs share many characteristics, suggesting the SP isolated from malignant tumors contains CSCs. STUDY DESIGN: Experimental Study. METHODS: The SP was isolated from a head and neck cancer cell line and analyzed for CSC-like characteristics. RESULTS: The SP demonstrated the ability to reproduce both SP and non-side population (NSP) cells from as few as one cell. The SP had lower expression of active β-catenin and more resistance to 5-fluorouracil; the SP also demonstrated greater expression of Bmi-1 (4.3-fold) and ABCG2 (1.4-fold). SP cells were able to produce tumors in an animal model, whereas NSP were not. SPs were identified in two primary human tumors. CONCLUSIONS: This work adds to the evidence that the SP in head and neck cancer represents cells with CSC properties and provides a method by which CSCs can be isolated and studied.