INSITU HYBRIDIZATION FOR EPIDERMAL GROWTH-FACTOR RECEPTOR (EGFR) EXTERNAL DOMAIN TRANSCRIPTS IN PROSTATIC ADENOCARCINOMA

We examined prostatic adenocarcinomas from 19 formalin fixed radical p rostatectomy specimens for EGFR by in situ hybridization employing a 2 4 base synthetic biotin-labeled oligonucleotide probe complementary to the 5' end of EGFR mRNA. All slides were examined by light microscopy using a 25x objective. Each field was given three values: 1) Gleason grade (1-5), 2) Nuclear grade [small (<5.0 mu), intermediate (5-10 mu) , large (>10 mu)], and 3) EGFR staining intensity score (0, absent; 1, weak; 2+, moderate to strong). A total 851 25x fields of prostatic ad enocarcinoma were studied. All cancers demonstrated at least some degr ee of cytoplasmic EGFR message. The EGFR intensity score correlated be st with tumor nuclear size. No correlation with Gleason grade was obse rved. Cytoplasmic staining was also identified in the basal cell layer of benign glands, high grade prostatic intraepithelial neoplasia, str omal nodules, transitional epithelium, periurethral glands, and gangli on cells. Competitive hybridization experiments using an unlabeled EGF R probe showed markedly diminished hybridization signal, while in situ hybridization with a biotin-labeled EGFR sense probe was negative. Im munohistochemistry on 13 of the tumors with 2 monoclonal antibodies ag ainst EGFR showed staining in only 1/13 and 10/13 tumors. EGFR express ion appears to be most prominent in tumors of high nuclear grade. Furt her studies will be necessary to explore this growth factor as a progn ostic variable in this tumor.