['A disintegrin and metalloprotease (ADAM) 9 has been implicated in tumour progression of prostate cancer. We evaluated the expression of ADAM9 on protein and messenger RNA (mRNA) level in a larger cohort of prostate cancer cases following prostatectomy and correlated the findings with clinicopathological parameters including prostate-specific antigen (PSA) relapse times.', 'We immunostained 198 clinicopathologically characterised prostate cancer cases for ADAM9. For 25 additional cases, ADAM9 mRNA of microdissected tumour and normal tissue was analysed via quantitative reverse transcriptase-polymerase chain reaction.', 'ADAM9 was significantly upregulated in prostate cancer compared with normal tissue on mRNA and protein level. ADAM9 protein expression was significantly associated with shortened PSA relapse-free survival in univariate and multivariate analyses, particularly in patients who had received prior androgen ablation.'] Is aDAM9 expression a significant and independent prognostic marker of PSA relapse in prostate cancer?