Immunohistochemical detection of p53 protein in archival tissues from squamous cell carcinomas of the oral cavity using wet autoclave antigen retrieval.

Using a panel of four anti-p53 antibodies (CM-1, PAb 1801, DO7, and PAb 240), the phenotypic characteristics of p53 protein overexpression were investigated in 22 routinely formalin-fixed and paraffin-embedded squamous cell carcinomas of the oral cavity. Conventional immunohistochemical staining without pretreatment for antigen retrieval was compared with wet autoclaving (AC) and microwave irradiation (MW). Applying AC or MW, p53 immunoreactivity was demonstrated in 9/22 cases with PAb 1801 and DO7 antibodies and in 8/22 cases with the CM-1 antibody. Immunostaining with the PAb 240 antibody after AC pretreatment showed p53 positivity in 8/22 tumours, but in only 4/22 following MW pretreatment. Immunostaining without pretreatment revealed only 2/22 p53-positive cases using CM-1, 4/22 with PAb 1801, and 3/22 with DO7. Without pretreatment, the PAb 240 antibody was consistently negative. Wet autoclave pretreatment was significantly superior for all the antibodies used in this study when compared with conventional immunohistochemistry without pretreatment (P < 0.005). It yielded better results than microwave irradiation for antigen unmasking in relation to the PAB 240 antibody (P < 0.05). Wet autoclave pretreatment is recommended as a reliable and highly reproducible method for p53 antigen retrieval in routinely processed archival material. The advantages over microwave pretreatment include simple handling and good preservation of morphology.