Immunohistochemistry, in situ hybridization and polymerase chain reaction (PCR) in detecting c-myc expression in human malignancies.

The assessment of oncogene expression at cellular level is important in understanding the role of those genes in carcinogenesis. Using in situ hybridization and immunohistochemistry, the expression of oncogenes can be visualized in topographic relation to tissue morphology. In the present study, c-myc overexpression was studied in ten carcinomas of different origin (6 mammary adenocarcinomas, 2 vulvar and 2 bronchial squamous cell carcinomas) by in situ hybridization (ISH) with 35S-labeled RNA probes and by immunohistochemistry (IHC). DNA amplification and transcription of c-myc oncogene were also studied with polymerase chain reaction (PCR) using beta-globin as an intrinsic standard for DNA amplification. The effect of formalin fixation of c-myc expression was simultaneously studied. Half of the tumours (5/10) demonstrated c-myc mRNA overexpression by ISH performed on frozen sections and two of the samples were shown to over-express c-myc protein by IHC. Only two samples fixed in formalin showed positive signals for c-myc mRNA. None of the biopsies showed DNA amplifications either with ISH or PCR. The present results suggest that ISH with RNA probes is a useful method for detecting the transcription of activated oncogenes in malignant tissues, especially when applied on frozen sections. The results also indicate that in some cases, c-myc gene may be adequately transcribed to mRNA but the latter is not translated to the appropriate oncoprotein.