p53, PCNA and Ki-67 expression in oral squamous cell carcinomas: the vagaries of fixation and microwave enhancement of immunocytochemistry.

Proliferation markers are widely used as indicators of tumour progression and aggression. Fixation and antigen retrieval methods may enhance the immunocytochemical sensitivity of these markers but may also lead to loss of specificity. As these methods are often used quantitatively, standardisation of internal and external methodology is paramount. This study aimed to compare the effects of alcohol and formalin fixation and of microwaving on the immunocytochemical demonstration of p53, PCNA and Ki-67 in oral squamous cell carcinoma using duplicate tissue blocks from 24 cases. Both qualitative and quantitative differences in antigen expression were revealed. Whilst alcohol fixation alone at least maintained and usually increased the strength of positive staining, microwaving alcohol-fixed sections often gave rise to non-specific staining. p53 staining following microwave enhancement of alcohol-fixed tissue showed a significant incidence of conversion of negative results to positive and of positive staining in unexpected tissue components. Alcohol fixation increased the sensitivity of PCNA detection with a far less dramatic loss of specificity. The results emphasise the need for careful standardisation of immunocytochemical methods, particularly when used quantitatively and for inter-laboratory comparisons.