Proliferating cell nuclear antigen counts as markers of cell proliferation in head and neck cancer.

Proliferating cell nuclear antigen (PCNA) expression was investigated immunhistochemically in 53 squamous cell carcinomas of the head and neck. PCNA is a 36-kDa nuclear protein associated with the cell cycle. Results were compared with Ki67 counts, with this latter marker used to demonstrate proliferative compartments. Overall, the PCNA and Ki67 labelling index showed a similar distribution pattern in normal and tumor tissue. A strong correlation was found to histological differentiation. There was no significant difference between PCNA and Ki67 counts (r = 0.8), and PCNA immunostaining allowed assessment of proliferative activity in the head and neck cancers studied. The application of formalin-fixed, paraffin-embedded tumor material demonstrated the advantage of this method and showed that it is an excellent alternative to Ki67 counts.