Diethylstilbestrol (DES) has a direct cellular mechanism inhibition on prostate cancer. Its action is independent from the oestrogen receptors and is preserved after a first-line hormonal therapy. We aimed to identify proteins involved in the direct cellular inhibition effects of DES on prostate cancer. We used a clonogenic assay to establish the median lethal concentration of DES on 22RV1 cells. 22RV1 cells were exposed to standard and DES-enriched medium. After extraction, protein expression levels were obtained by two-dimensional differential in-gel electrophoresis (2D-DIGE) and isotope labelling tags for relative and absolute quantification (iTRAQ). Proteins of interest were analysed by quantitative RT-PCR and western blotting. The differentially regulated proteins (P<0.01) were interrogated against a global molecular network based on the ingenuity knowledge base. The 2D-DIGE analyses revealed DES-induced expression changes for 14 proteins (>1.3 fold; P<0.05). The iTRAQ analyses allowed the identification of 895 proteins. Among these proteins, 65 had a modified expression due to DES exposure (i.e., 23 overexpressed and 42 underexpressed). Most of these proteins were implicated in apoptosis and redox processes and had a predicted mitochondrial expression. Additionally, ingenuity pathway analysis placed the OAT and HSBP1 genes at the centre of a highly significant network. RT-PCR confirmed the overexpression of OAT (P=0.006) and HSPB1 (P=0.046).