Prostate cancer (PCa) is the second most common cancer in men and negatively impact muscle mass, physical function, and patient-reported outcomes. Androgen deprivation therapy (ADT) is a widely used treatment for advanced disease, but it exacerbates these adverse effects. To investigate the molecular mechanisms underlying these changes in skeletal muscle, we performed muscle biopsies of the vastus lateralis for proteomic analysis from nineteen patients with PCa before starting ADT and after six months of treatment.