Proliferation index of different subtypes of human primary nasopharyngeal carcinoma (NPC) A, Triple-immunolabeling was performed using anti-Ki-67 (green), anti-MCM2 (purple), and anti-PCNA (red) in human primary NPC. Nuclei were counterstained by DAPI (blue). Top panel: low magnification; bottom panel: high magnification. B, Sections of different subtypes of primary NPC were immunostained using anti-Ki-67 antibody. Top panel: low magnification; bottom panel: high magnification. C, Ki-67-positive cells in different subtypes of primary NPC were calculated as the percentage of all tumour cells that were Ki-67-immunopositive cells. Data are mean value ± SEM. K-NPC = keratinizing NPC; NK-NPC = nonkeratinizing NPC; UN-NPC = undifferentiated NPC.