Interestingly, the percentage of Ki67 + tumour cells was higher in the more aggressive 4T1 samples compared to 66cl4 (Fig. 5E; percentage of Ki67 + tumour cells among total tumour cells: 66cl4: 41.13%; 4T1: 80.65%; 4T1-liver: 63.47%). This evidence concerns the gene MKI67 and neoplasm.