MKI67 and nasopharyngeal carcinoma: In NPC treated with shRNA targeted against p21, the percentage of Ki67+ proliferating neuronal precursors was increased significantly (from 26.4 ±5.8% t0 40.2±5.1%, respectively, p<0.05), and at the same time the percentage of p21+ cells was decreased (40.83±5.3% to 22.67±1.9%, respectively, p<0.05 for both) (Fig. 4B and C), confirming that when p21 is suppressed the proliferation of neuronal progenitors is increased.