In vivo, the combination of DT2216 and AZD8055 strongly inhibited the growth of cell line-derived and patient-derived xenograft (PDX) tumors and reduced tumor burden as well as increased survival of a murine Rb1/p53/p130 SCLC genetically engineered mouse (GEM) model without causing appreciable thrombocytopenia or other normal tissue injuries. The gene discussed is RB1; the disease is small cell lung carcinoma.