OVEREXPRESSION OF P-GLYCOPROTEIN IN UNTREATED AFP-PRODUCING GASTRIC-CARCINOMA

P-glycoprotein (P-gly), which is responsible for the phenotypic expres sion of multidrug resistance in cancerous tissue was stained immunohis tochemically in previously untreated alpha-fetoprotein (AFP)-producing (n = 20) and nonproducing gastric cancers (n = 20). P-gly, AEP, and c arcinoembryonic antigen(CEA) were stained in formalin-fixed paraffin-e mbedded tissue sections immunohistochemically using the monoclonal ant ibody JSB-1, anti-AFP, and anti-CEA, respectively. DNA ploidy pattern was determined by Fluorescence Activated Cell Sorter (FAGS) analyzer. P-gly was significantly overexpressed in AFP producing gastric cancers (60%) than in AFP nonproducing ones (20%) (P < 0.01). When the result of P-gly staining was analyzed among the AFP-positive cases, P-gly po sitivity did not emerge either as a significant prognostic factor or a s a predictor of the metastatic potentiality of the tumor. The intrins ic overexpression of P-gly in AFP producing gastric cancers proves its biological and morphological similarities to hepatocellular carcinoma . The significantly (P < 0.05) higher incidence of P-gly in diploid tu mors indicate that expression of this phenotype might be related to th e differentiation of the tumor. P-gly was overexpressed in AFP produci ng gastric carcinoma and the existing drug resistance, frequent recurr ence, and poor prognosis might be explained by presence of P-gly in th is carcinoma. (C) 1995 Wiley-Liss, Inc.