We attempted to validate our models in independent cohorts but were limited by a lack of publicly available cohorts with all the molecular features and relevant clinical data on previous ipilimumab therapy and biopsy timing used in our integrated model . In a limited validation , we tested predictive models incorporating individual features where data were available in an independent validation cohort 44 ( Methods ) , and found concordant predictions of primary resistance with low MHC - II HLA expression in ipilimumab - treated tumors and higher heterogeneity in ipilimumabnaive tumors ( Extended Data Fig . 10 ) , although neither of these predictors was significant in this small cohort ( empiric P = 0.21 and P = 0.066 , respectively ; Methods ) .