Background: p63 is a homologue of the tumour suppressor gene p53, which is expressed in human basal squamous epithelium. Some investigators maintain that p63 plays a role in the development of squamous epithelium and, despite its homology to p53, it is considered to act as an oncogene. This study investigated the expression of p63 in conjunctival intraepithelial neoplasia of different grades, and conjunctival squamous cell carcinoma and its correlation to the proliferation marker MIB-1.
Material and methods: Seventeen conjunctival specimens excised with the suspicion of either conjunctival intraepithelial neoplasia (CIN) or squamous cell carcinoma were diagnosed histologically as follows: 2 squamous cell carcinomas of the conjunctiva, 2 CIN grade I, 3 CIN grade II, 7 CIN grade III, 2 CIN with beginning invasion and 1 normal conjunctiva with no dysplasia. Sixteen microscopically-normal postmortem conjunctival specimens and normal conjunctiva, CIN and carcinoma specimens were stained immunohistochemically with antibodies against p63 and MIB-1. At least 500 cells per specimen were counted and the percentage of positively-stained cells of each antibody was calculated.
Results: A mean of 80% (57-89%) of the dysplastic cells from the CIN specimens stained positively with antibodies against p63, especially in the lower two-thirds of the epithelium, statistically significantly more compared with the normal specimens (9-55%, mean 36%, p<0.001). Nevertheless, we did not find a correlation between the percentage of p63-positive cells and the differentiation grade of the malignant specimens. MIB-1 positivity was shown by 0-1% of the cells in the normal postmortem controls, by 3-30% (mean 12%) of the cells in the basal and occasionally in the middle layer of the CIN specimens, and 16-61% (mean 23%) in the carcinoma specimens.
Conclusion: In conjunctival intraepithelial neoplasia and squamous cell carcinoma of the conjunctiva, p63 is preferentially expressed in the immature dysplastic epithelial cells. Its staining does not correlate with MIB-1-expression, and therefore does not appear to be linked to cell proliferation.