Therefore, PRISM-SRM assays can be adapted to detect ERG protein in cells present in clinical specimens (e.g., tissue, post-DRE urine, and circulating tumor cells in blood), and cell-free ERG protein present in the blood sera, providing an opportunity for its use in the clinical setting for detection in prostate cancer patients, and define treatment strategies in accordance. The gene discussed is ERG; the disease is prostate cancer.