For over 20 years, scientists have proposed various roles for prominin-1, including its function as a stem cell and cancer stem cell biomarker, its involvement in organizing plasma–membrane protrusions, maintaining the apical-basal polarity of epithelial cells, biogenesis of the photoreceptive disc, mechanism of multidrug resistance, and the capacity for self-renewal and tumor formation [98]. The gene discussed is PROM1; the disease is neoplasm.