U2AF1 and myelodysplastic syndrome: An early mechanism class to to be recognized is the sensitivity of tumor cells bearing spliceosomal mutations, for example chronic lymphocytic leukemia (CLL) cells bearing SF3B1 mutations, [21] and myelodysplastic syndrome (MDS) cells carrying U2AF1 mutations.[22] Additionally, it was found that tumors driven by MYC[23] or KRAS[24] are also sensitized to this class of drugs.