P53 EXPRESSION IN FORMALIN-FIXED, PARAFFIN-EMBEDDED ARCHIVAL SPECIMENS OF INTRAHEPATIC CHOLANGIOCARCINOMA - RETRIEVAL OF P53 ANTIGENICITY BY MICROWAVE-OVEN HEATING OF TISSUE-SECTIONS

Immunohistochemical demonstration of p53 is thought to reflect mutatio ns of the p53 gene. Although p53 expression or mutation has been inves tigated in a variety of carcinomas, it has not been examined in intrah epatic cholangiocarcinoma (CC). We investigated expression of p53 in f ormalin-fixed, paraffin-embedded archival specimens of 40 CCs (22 auto psy cases and 18 surgical cases) by immunohistochemistry using four an tibodies (PAb1801, DO-7, BP53-12, CM1). We also attempted to enhance p 53 expression by pretreatments of tissue sections by pepsin digestion as well as by microwave oven heating. Formalin-fixed, paraffin-embedde d archival surgical specimens of 15 colon carcinomas were used as cont rols. In surgical cases, p53 expression was abolished by pepsin predig estion, although it was greatly enhanced by pretreatment of microwave oven heating in all immunostainings (PAb1SO1, DO-7, BP53-12, CM1). In surgical cases immunostained with microwave oven heating, DO-7, BP53-1 2, and CM1 showed frequent p53 expression (22% in CC; 60-67% in colon carcinoma), whereas PAb1801 showed low p53 expression (0% in CC; 13% i n colon carcinoma). In contrast to the surgical cases, all 22 CCs of a utopsy cases showed no p53 expression by any antibodies as well as by any pretreatments. These results shows that a pretreatment of tissue s ections by microwave oven heating is a very good method for demonstrat ing p53 protein in formalin-fixed, paraffin-embedded archival material s and that DO-7, BP53-12, and CM1 are useful antibodies for detection of p53 in formalin-fixed, paraffin-embedded archival materials. No exp ression of p53 in autopsy cases of CC suggests that p53 antigenicity i s lost during autopsy procedure. The data also suggest that approximat ely 22% of CC shows p53 mutation. Thus, p53 mutation may be involved i n carcinogenesis of some of CC.