Prostate cancer (PCa) is the most common malignancy among men in the USA. Polyphenon E (PolyE) is a standardized blend of polyphenols found in green tea extract, which has been shown to have chemoprevention value in PCa models, but the molecular mechanism(s) have not been elucidated. Polyphenols from green tea are known to alter the expression levels of some genes. Our experimental goal was to identify genes with expression level changes (up- or down-regulated by 2-fold or more) in normal, primary prostate cells as well as two PCa cell lines, DU145 and PC-3. Ultimately, we sought to identify genes whose expression level was differentially altered by PolyE treatment in normal versus PCa cells. We hypothesized that exposure to PolyE induces gene expression changes, which could provide rationales for the molecular mechanism(s) and provide potential targets for therapeutics and detection. A non-cancerous, human primary prostate cell line as well as two PCa cell lines (DU145 and PC-3) were cultured and treated them with varied concentrations of PolyE for 24 hours. Cellular RNA was isolated and subjected to microarray analyses (MA) at the Molecular Genomic Core facility of the Moffitt Cancer Center. A plethora of genes were identified by MA as having two-fold or higher gene expression level changes after PolyE exposure. Of these genes, fourteen with were selected for further analyses by TaqMan qRT-PCR. Cellular RNAs were converted into cDNA used in validated TaqMan qRT-PCR assays (StepOneTM RT-PCR System). RT-PCR data was analyzed using StepOneTM software and the ΔΔCt method. ACTB served as the endogenous control gene for all TaqMan qRT-PCR assays. Our qRT-PCR data from PolyE-treated DU145, PC-3, and primary prostate cells were consistent in the lack of expression changes greater than 2-fold for ATM, CASP8, HDAC4 and RB1. For RGCC, MXD1, CCSER2/FAM190B, CBLB and BCL2L11, gene expression levels increased by more than 2-fold in all three cell lines. For CCNB1 and SEC62, primary cells experienced more than a 2-fold change in gene expression, while the DU145 and PC-3 cell lines did not. Interestingly, ATM gene expression levels decreased by more than 10-fold in primary prostate cells, but in DU145 and PC-3 had changed less than 3-fold. Most notably, RGS4 gene expression levels were differentially altered in primary prostate cells compared to the PCa lines. In primary prostate cells, RGS4 decreased by more than 7-fold, but experienced a greater than 10-fold increases in DU145 and PC-3. In summary, we have identified RGS4 as a gene whose expression levels are differentially affected in primary prostate cells versus the PCa cell lines DU145 and PC-3. Citation Format: L. Michael Carastro, Ricardo A. Cordova, Daniel A. Barboto, Ricardo A. Declet-Bauzo, Irena Gushterova, Nicholas K. Lago, Nicholas E. Braganca, Joanna C. Burr, Dara E. Hoffman, Jong Y. Park. Gene expression changes in Polyphenon E treated prostate cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4211. doi:10.1158/1538-7445.AM2017-4211