The sources of selection bias were the site of tumor origin (SMD, 0.84; standardized bias, 86.4%), functioning tumor status (SMD, 0.29; standardized bias, 30.4%), WHO grade (SMD, 0.38; standardized bias, 85.3%), the Ki-67 proliferation index with a 10% cutoff (SMD, 0.33; standardized bias, 40.3%), surgery for primary tumors (SMD, 0.47; standardized bias, 45.4%), the mean number of PRRT cycles (SMD, 0.49; standardized bias, 50.8%), and the type of radionuclide (SMD, 0.40; standardized bias, 16.3%). This evidence concerns the gene MKI67 and neoplasm.