The addition of alisertib to irinotecan in KRAS mutant PDX models demonstrated near additive to synergistic effects in 4 out 5 tumor types tested (CUCRC042 average ψ = 0.8, CUCRC098 average ψ = 0.7, CUCRC102 average ψ = 1.5 and CUCRC108 average ψ = 0.7) and a less than additive effect in one model (CUCRC007 average ψ = 0.5). This evidence concerns the gene KRAS and neoplasm.