The most utilized targeted therapies in colorectal cancer (CRC) are focused on EGFR inhibition and anti-angiogenesis. In the ~5% of patients with microsatellite instability (MSI-H) or high tumor mutational burden (TMB), checkpoint inhibitors (CPIs) have been approved. Oncxerna has developed an RNA expression-based approach to characterize the ‘dominant' biology of a patient's tumor microenvironment with the diagnostic hypothesis to prospectively pair those patients with therapies and known mechanism of action that directly target these biologies. We developed an RNA-based gene expression panel (TME Panel-1) and machine learning (ML) algorithms to prospectively predict a patient's response to anti-angiogenesis or immune modulators, such as CPIs. In this study, we explore the potential of the TME Panel-1 to identify dominant biologies present in colorectal cancer specimens procured from the Wood-Hudson Cancer Research Lab. Total RNA expression counts from FFPE slides were analyzed with the ML algorithms and used to assign each sample into one of four subgroups. The respective prevalence of the subgroups are similar to those observed in gastric cancer and ovarian cancer samples, suggesting that the TME-Panel 1 has potential to be used to develop pan-tumor diagnostics. We will present these results, correlations with clinical outcomes and other relevant biomarkers for CRC. In summary, we conclude that RNA-based descriptors of biology may be a useful approach to enrich for better response to targeted therapies whose mechanism of action is to modify the TME biology. Citation Format: Kristen Strand-Tibbitts, Kerry Culm-Merdek, Valerie Chamberlain Santps, Laura Benjamin, Julia Carter, Larry Douglass, Roman Luštrik, Robert Cvitkovič, Luka Ausec, Rafael Rosengarten. Development of an RNA based diagnostic panel to the tumor microenvironment to match cancer therapies for colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 348.