The present invention features methods for increasing sensitivity and/or reversing resistance to chemotherapy, methods for treating or preventing a cancer in a subject, methods for treating clonal hematopoiesis of indeterminate potential in a subject, and methods of identifying resistance or sensitivity to chemotherapy in a subject. In some embodiments, the methods contain the step of administering an agent that inhibits the expression or activity of a Protein phosphatase 1D (PPM1D) polypeptide or polynucleotide. The present invention also features compositions for increasing sensitivity and/or reversing resistance to chemotherapy.