Cadherins seem to play and important role in prostate cancer (PCa) progression. E-cadherin loss of expression has been associated with poor prognosis; P-cadherin's role is still elusive. Although pT3 PCa is often considered "high-risk cancer," it does not exhibit an uniformly poor prognosis. Herein, we assessed the prognostic value and survival impact of E-cadherin and P-cadherin immunoexpression in pT3 PCa. Radical prostatectomy (RP) specimens from 102 pT3 PCa patients treated between 1991 and 2014 in a single institution were designated for E-cadherin and P-cadherin immunoexpression analysis. A representative block from each specimen was selected for tissue micro-array (TMA) construction, using 3 cores per case. E-cadherin immunoexpression was assessed via a digital image analysis system. For P-cadherin, scoring criteria for HER2 in gastric cancer were used. Clinical records of all patients were reviewed for baseline clinical/pathologic characteristics and follow-up data. E-cadherin-low PCa patients displayed worse disease-specific survival (DSS), although not reaching statistical significance (HR 2.65, 95%CI 0.81-7.88). However, considering the pT3b group only, those with low E-cadherin immunoexpression displayed significantly worse overall-survival (OS) and DSS (HR 3.69, 95%CI 1.18-11.50; HR 5.90, 95%CI 1.40-24.81). No significant differences in survival were found for P-cadherin differential immunoexpression. Furthermore, an association between E-cadherin and P-cadherin immunoexpression (p = 0.019) was found, as among E-cadherin-low PCa, 96.6% were P-cadherin negative. We demonstrated that low E-cadherin immunoexpression discriminates among pT3b PCa patients those with poorer survival and which might benefit from specific therapy. The role of P-cadherin in PCa seems context-dependent deserving further investigation.