MKI67 and cancer: To evaluate whether lung tissue of Cre- and Cre+ mice had greater evidence of cancer cell infiltration, lung tissue was immunolabelled with Ki67, a marker of proliferating cells, and separated into high (> 50%) and low (< 50%) groups revealing a similar number of mice with high levels of Ki67 staining in Cre- (50%) and Cre+ mice (38%) (Figure 6D, 6E).