Comparison of immunostainings for proliferating cell nuclear antigen and Ki-67 in human extraocular lesions

• Background: Cell kinetic information is helpful to understand disease progression, treatment response, and prognosis of the neoplasms. To compare the usefulness and limitations of antibodies that recognize the cell cycle-associated molecules, proliferating cell nuclear antigen (PCNA) and Ki-67, we performed immunostaining in formalin-fixed, paraffin-embedded tissue sections of extraocular lesions. • Methods: Specimens were obtained from patients undergoing routine surgical procedures. Formalin-fixed, paraffin-embedded sections were stained for PCNA and Ki-67 using the monoclonal antibodies PC10 and MIB-1, respectively. Microwave oven heating for antigen retrieval was performed before immunostaining. • Results: In squamous cell carcinomas and basal cell carcinomas, PCNA immunostaining varied greatly. Basal cells of benign epithelial lesions showed moderate to weak PCNA staining. Strong PCNA immunoreactivity was demonstrated in foci of inflammation and germinal centers. Microwave processing enhanced the intensity of those PCNA immunostainings. As the PCNA immunostaining intensity had a great variability, the absolute numbers of PCNA-positive cells were hard to count in some tissues. High Ki-67 counts were observed in squamous cell carcinomas, foci of inflammatory cells, and germinal center cells. Basal cell carcinomas and benign lesions showed low Ki-67 counts. Every section showed clear nuclear staining in Ki-67 immunostaining. • Conclusion: Careful consideration is required in the assessment of cell proliferation using PCNA. The immunostaining of Ki-67 may be more accurate than that of PCNA for evaluating cell proliferation in formalin-fixed, paraffin-embedded tissues.