The present invention relates to methods to treat or prevent cancers in a subject, in particular the present invention relates to a method of treating and/or preventing cancer comprising targeting cancer stem cells by administering miRNAs which have reduced expression or are lacking in the cancer stem cells. In some embodiments, the miRNAs that are reduced or lacking in cancer stem cells are let-7 miRNAs. In alternative embodiments, the present invention relates to a method of treating and/or preventing cancer comprising targeting cancer stem cells by administering miRNAs which have increased expression levels in the cancer stem cells. Another aspect of the present invention relates to methods to enrich for a cancer stem cell population. Another aspect of the present invention relates to methods to identify miRNAs which contribute to the self-renewal capacity of cancer stem cells.