Discrepancies between detection of Bcl-2 by in situ hybridization and immunocytochemistry in human prostate cancer tissues

Extensive study of Bcl-2 protein expression in prostate cancer (CaP) tissues by means of immunocytochemistry (IC) has provided evidence that it positively correlates with high grade and stage of CaP and is associated with resistance to anti-androgen hormone therapy. In the present study, we investigated the expression of bcl-2 mRNA by non-isotopic in situ hybridization (ISH) in a series of 36 CaP with or without previous anti-androgen hormone treatment and performed a comparison with IC-detected Bcl-2 protein expression. Expression of Bcl-2 mRNA detected by ISH consistently differed from that detected by IC, especially in lymph node metastases (whereas no relevant variations of Bcl-2 mRNA levels were found in treated vs. untreated CaP patients). In particular, high content of Bcl-2 mRNA was found in 25/36 cases of CaP (in 13/18 hormone-treated and 12/18 untreated patients). Conversely, Bcl-2+ immunostaining was observed in only 7/36 CaP (in 4/18 hormone-treated and 3/18 untreated patients). Furthermore, ISH revealed Bcl-2 mRNA in 4/7 lymph node metastases, all 7 of which were Bcl-2(-) by IC. We conclude that, in the absence of a demonstrated post-transcriptional control of the bcl-2 gene, detection of mRNA by ISH in prostate archival tissues appears to be a reliable alternative method to assess differential expressions of the bcl-2 gene.