The implementation of microarray (cDNA and oligonucleotide) technology is enabling investigators to assess gene expression at a tissue/cellular level by quantification of messenger RNA (mRNA) transcripts. Once assimilated, these data should provide gene-expression profiles that are unique to specific cells, their responses to specific stimuli, and also help unravel complex signalling pathways. With regards to a more holistic approach, comparisons between diseased and normal tissues could identify genes that are directly implicated in the disease pathology and hence identify targets for therapeutic intervention. However, as with all systems, there remains the possibility of generating false positives and, therefore, differential gene expression should be verified using other techniques such as real-time PCR with reverse-transcription or Northern blot analysis. Furthermore, certain genes can be upregulated without an increase in actual protein levels and, therefore, the use of tissue microarray technology allows high-throughput immunostaining to correlate protein and mRNA data.These technologies have recently been applied to dissect the molecular basis of the most common malignancy in men (with the exception of non-melanoma skin cancer) – prostate cancer. Dhanasekaran et al. 1xDelineation of prognostic biomarkers in prostate cancer. Dhanasekaran, S.M. et al. Nature. 2001; 412: 822–826Crossref | PubMed | Scopus (1213)See all References1 have used both cDNA and tissue microarrays to great effect in comparing and characterising gene-expression profiles in normal and neoplastic prostate specimens. Having generated a vast amount of data, the authors focused on the hepsin and PIM1 genes that encode a transmembrane protease and serine/threonine kinase respectively. Both proteins are overexpressed in prostate tumours and interestingly PIM1 appears to be co-regulated with the oncogene MYC, supporting the possibility of a synergistic oncogenic effect. Interestingly, immunostaining revealed that metastatic prostate samples expressed hepsin at levels in between malignant and benign prostate tumours. Men with elevated prostate-specific antigen (PSA) levels – a clinical marker for prostate cancer – are prone to die from metastases following radical prostatectomy. Extensive statistical analyses subsequently revealed that men conforming to this group have low or absent hepsin protein levels. The same trend was also demonstrated for PIM1 indicating that these two proteins can now be considered as additional clinical biomarkers for prostate cancer.In the past few months, there has been an array of similar studies reporting on the application of the expression array technology to study prostate cancer. Two such studies also identified hepsin as a useful biomarker 2xHuman prostate cancer and benign prostatic hyperplasia: molecular dissection by gene expression profiling. Luo, J. et al. Cancer Res. 2001; 61: 4683–4688PubMedSee all References, 3xExpression profiling reveals hepsin overexpression in prostate cancer. Magee, J.A. et al. Cancer Res. 2001; 61: 5692–5696PubMedSee all References. Further mining of all these microarray data sets will lead to the generation of a large panel of useful biomarkers to aid in the detection and prognosis of prostate cancer. In addition, they could also reveal new ‘molecular targets’ for potential therapeutic intervention towards improved treatment and management of this malignancy.