Enhanced expression of the c-myc protooncogene in high-grade human prostate cancers.

We examined a series of 29 surgical specimens of benign and malignant human prostate tissue for the expression of both the cHa-ras and c-myc protooncogenes. Northern blots were prepared using polyadenylated mRNA extracted from nine prostatic adenocarcinomas, 19 benign hypertrophied prostates (BPH) and one normal prostate. When the Northern blots were hybridized to a probe for cHa-ras, only one specimen of BPH showed an appreciable amount of the 1.2-kb transcript homologous to cHa-ras. Upon reprobing these blots with c-myc, six cancers showed a considerable amount of a 2.4-kb transcript homologous to c-myc. Three other cancers and all the benign tissue showed little or no detectable 2.4-kb c-myc transcript. On retrospective analysis, the cancers with elevated c-myc transcripts were found to have a Gleason score of 5 and above (poorly differentiated tumors), while the cancers with little or no c-myc transcripts were all of Gleason score 4 and lower. Finally, we compared our ability to detect c-myc transcripts in mRNA extracted from a surgically derived prostate tumor with mRNA extracted from the same tumor subject to a sham electrocautery procedure, as would occur during transurethral resection. The electrocautery procedure decreased both the intensity and the integrity of the c-myc signal in mRNA from the tumor. Thus, our exclusive use of surgically derived prostate tumors may be the reason we are able to detect an elevation in the expression of c-myc mRNA in high-grade tumors.