PROJECT SUMMARY / ABSTRACT The proposed research applies scientific advancements in cancer biology and biotechnology to reduce the pain and suffering caused by prostate cancer. The current approach to prostate cancer diagnosis involves screening with prostate serum antigen (PSA), a low specificity assay with a significant false positive rate. In current screening practice, men with elevated PSA are referred for transrectal biopsy, which is an invasive procedure associated with risk of serious complications. However, as a result of limited PSA performance, only 10-15% of the one million biopsies performed annually will detect clinically significant cancer. Better diagnostic tools would eliminate the need for biopsy in the majority of cases. In Phase I, we show that measuring the urine levels of two cancer-specific genes, the TMPRSS2:ERG (T2:ERG) fusion and PCA3, serve as a highly accurate biomarker assay. In our proof-of-concept work we successfully: (i) validated diagnostic performance for urine levels of T2:ERG, (ii) developed an algorithm combining urine levels of PCA3 and T2:ERG with serum PSA to generate the MPS risk score, (iii) validated performance of MPS in a 1,225 patient cohort, determined the model used for the MPS assay, and demonstrated its ability to prevent 28% of biopsies with >98% accuracy, and (iv) shifted the assay from a limited-throughput proprietary platform to a more cost-effective qPCR method that enables integration of additional targets. Current attempts to fill this clinical need perform poorly, are understudied in key populations, and have low specificity for high-grade cancer. To have maximal impact and continue to work towards commercialization, we will study MPS in these increasingly pertinent contexts in Phase II. In Aim 1 we characterize performance of MPS in relation to multi-parametric MRI, an imaging technology that has become prominent in the prostate cancer diagnostic workflow. The capacity of biomarkers to either replace or work synergistically with mpMRI has not been sufficiently described. In Aim 2 we identify and validate optimal parameters for MPS testing in African Americans, a demographic with elevated cancer incidence and mortality. In Aim 3 we integrate additional biomarkers to better distinguish between low-grade and high-grade cancers. Instead of being treated, men with low-grade caner are often serially monitored with burdensome procedures including biopsy. Biomarker genes used now are not specific to high-grade cancer, thus an improved assay including such high- grade associated genes is needed. Given the prevalence of prostate cancer resulting in one million prostate biopsies each year, and the potential for improvement over the currently flawed diagnostic approach, this clinically impactful work has great promise as a successful commercial opportunity.