The disclosure provides methods for predicting and/or determining whether a subject has cancer based on the level of expression of miR-18b. The disclosure also provides methods for determining whether a cancer in a subject is progressing or regressing based upon the change of expression levels of miR-18b between two time points. The disclosure further provides methods to treat a subject with a cancer by administering a polynucleotide comprising miR-18b and/or an agent that enhances the expression of miR-18b.