['Stem cells are postulated to mediate prostate cancer progression, and represent a small fraction of the entire tumor. Various proteins (α2-integrin, α6-integrin, CD117, CD133, EZH2, OCT3/4) are associated with a prostate cancer stem cell phenotype in cell lines and xenografts. Our objective was to investigate expression of stem cell markers in clinical prostate cancer in relation to outcome.', 'We validated immunohistochemical expression of stem cell markers in 481 prostate cancer patients and correlated expression with clinicopathologic parameters.', 'Sporadic expression of α2-integrin was present in a fraction of tumor cells (<5%) in 94.7% of tumors and associated with PSA\u2009>\u200910\u2009ng/ml (P\u2009=\u20090.04). α6-Integrin expression (<5%) occurred in 28.4% patients, while ≥5% α6-integrin expression was associated with PSA≤10\u2009ng/ml (P\u2009=\u20090.01), Gleason score <7 (P\u2009<\u20090.01) and pT2-disease (P\u2009=\u20090.02). α6-integrin was predictive for biochemical recurrence (P\u2009<\u20090.01), local recurrence (P\u2009=\u20090.03) and disease specific death (P\u2009=\u20090.03). EZH2 expression was generally low with 2.6% of tumors showing ≥1% positive cells. EZH2 was associated with Gleason score ≥7 (P\u2009=\u20090.01) and biochemical recurrence (P\u2009=\u20090.01). We did not identify expression of CD117, CD133, and OCT3/4 in prostate cancer samples.'] Is validation of stem cell markers in clinical prostate cancer : α6-integrin predictive for non-aggressive disease?