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. The gene discussed is U2AF1; the disease is B-cell chronic lymphocytic leukemia.