MSI2 and lung adenocarcinoma: To determine if Msi2 not only marks a cell with an enhanced capacity for lung adenocarcinoma growth, but whether it may also be required for initiation of these tumors, we compared wild-type and Msi2-knockout KrasG12D/+; Trp53fl/fl mice (Msi2−/−; KrasG12D/+; Trp53fl/fl) (Figure 3A).