MKI67 and neoplasm: To explore the effect of loss of wild-type Ras genes on tumor characteristics, 6 to 10 lung lesions from urethane-treated mice with the two extreme genotypes, namely Hras+/+;Nras+/+ versus Hras-/-;Nras-/-, were stained for markers of apoptosis (cleaved caspase 3), proliferation (Ki67), inflammation (F480), and Ras signaling (phosphorylated ERK and AKT).