['Progression to a lethal androgen-independent (AI) stage of advanced prostate cancer is a critical clinical obstacle limiting patient survival. PTEN inactivation is frequently observed in advanced prostate cancer and correlates with a poor prognosis. However, the functional significance of PTEN inactivation in AI progression has not been demonstrated.', 'PTEN expression was examined in benign, hormone naïve and AI human prostate cancer specimens, and in recurrent AI Shionogi tumors. The effect of antisense oligonucleotide (ASO)-mediated PTEN downregulation in AI progression of the Shionogi tumor model was determined.', 'Significantly reduced PTEN expression was observed in AI versus benign and hormone naïve prostate tumors. Seven of 14 AI Shionogi tumors exhibited marked downregulation or complete loss of PTEN. ASO-mediated PTEN inhibition reduced androgen-withdrawal induced regression of Shionogi tumors and accelerated AI progression.'] Is loss of PTEN associated with progression to androgen independence?