PROM1 and breast cancer: Consistently, inhibition of miR-9 and miR-221 reduced the proportion and tumor-sphere formation of BCSCs by reducing the expression of the stemness markers Nanog, CD133 and Oct4. Moreover, increased levels of miR-9 and miR-221 in BC are closely related to elevated risk of progression to malignancy, poor differentiation, lymph-node metastasis, reduced survival, late-stage evolution and increased tumor size [37].