Proliferating cell nuclear antigen (PCNA) expression in pseudoepitheliomatous hyperplasia, keratoacanthoma and squamous cell carcinoma of the skin.

Using immunohistochemical method the expression of proliferating cell nuclear antigen (PCNA), a marker of cell proliferation, was studied semiquantitatively in 9 cases of pseudoepitheliomatous hyperplasia (PEH), 24 cases of keratoacanthoma (KA), 47 cases of squamous cell carcinoma (SCC) and 5 cases of Bowen's disease (BD). It was observed that the distribution was marginal in PEH, KA and well-differentiated SCC (WDSCC), and diffuse in poorly-differentiated SCC (PDSCC) and BD. The staining pattern of BD was unusual in that the basal cells were often spared. While the PCNA expression of PEH and KA showed no significant difference from that of WDSCC, it was however significantly different (P < 0.05) from that of PDSCC and BD. The number of PCNA-positive cells in proliferating KA was more than that of regressing KA (P < 0.05). There was a positive correlation between the extent of PCNA expression and the grade of invasive SCC. It is concluded that the distribution and extent of PCNA expression is closely similar among PEH, KA and WDSCC and between PDSCC and BD, but their biological behaviour is different. Therefore while PCNA is a good indicator of proliferating cell pool, it is not an index of biological behaviour which is a genetic function of cells. However, the positive correlation between the extent of PCNA expression and the grade of invasive SCC is an indication of the size of the proliferating malignant cell pool which can have bearing on the biological behaviour of the tumour.