Abstract Purpose: Cervical adenocarcinomas (CAC), a less common cervical cancer histology with poor prognosis as compared to squamous cell carcinoma (CSCC), disproportionally present at advanced stages in young women and incidence is increasing; however, the same chemoradiation (CRT) paradigm is used by clinicians for both histologies. Given the rarity of CAC, little is known about genomic pathways and tumoral immune factors that differentiate CAC from CSCC and could drive differences in patient outcomes. Objective: To identify distinctions in the mutational landscape and immune phenotype of CAC and CSCC tumors in patients undergoing CRT which may be potential therapeutic targets. Methods: 80 patients with FIGO stage IB-IVA cervical cancer who underwent definitive CRT were prospectively enrolled on an IRB approved clinical trial. Cervical tumor DNA (9 CAC patients; 58 CSCC patients) and cervical tumor microenvironment samples (13 CAC patients, 67 CSCC patients) were collected by a noninvasive swab technique at baseline, and after 1, 3, and 5 weeks of CRT. WES and neoantigen prediction were performed and tumor mutation burden (TMB) was calculated as the number of somatic coding mutations per megabase. Lymphocyte immunostaining was performed according to standard protocols and cells were analyzed using a LSRFortessa X-20 Flow Cytometer (BD Biosciences) and FlowJo 10.6.1. Statistical comparison of mean values was performed by t-test. Results: Baseline mean TMB and tumor neoantigen was lower in CAC compared to CSCC (1.1±0.14 vs 5.2±3.5 respectively for TMB, p<0.01; 6.0±8.5 vs 455.3±472.5 respectively for neoantigen, p<0.01) and persisted during CRT. The top 3 most frequently altered genes unique to CAC were GPR98, SLC12A3, and TP53. The baseline mutational profile of CAC tumors was most similar to other adenocarcinomas including prostate and pancreatic cancer in TCGA. There was a significant reduction for CAC in baseline CD4+ T-cell infiltration in CAC compared to CSCC (p=0.01) which persisted through the course of CRT (p=0.02 at week 3). There was a trend toward decreased CD4+ T-cell activation, including co-expressing CD69 (p=0.17) and Ki67 (p=0.06), decreased CD8+ T-cell infiltration (p=0.19), and decreased Ki67+CD8+ T-cells as compared to CSCC (p=0.02). Conclusions: In contrast to CSCC, immune profiling of the CAC tumor microenvironment suggests a reduction in immune cell infiltrate and absence of or failed T-cell activation. Similarly, unique genetic alterations were detected between histologies, and CAC tumors displayed reduced TMB and loss of tumor neoantigen expression. These findings are consistent with an “immune cold” phenotype in CAC. These patients may be less likely to benefit from immunotherapy. Future investigation into molecularly targeted therapies or strategies that help mobilize peritumoral T-cells in response to CRT may better potentiate improved CRT response in CAC. Citation Format: Julianna Bronk, Xiaogang Wu, Rui Wang, Ananta Yanamandra, Tatiana Karpinets, Chike Abana, Molly El Alam, Katarina Tomasic, Daniel Lin, Erica Lynn, David Lo, Timothy Harris, Xingzhi Song, Andrew Futreal, Jianhua Zhang, Jagannadha Sastry, Ann Klopp, Lauren Colbert. Whole exome sequencing and immune profiling of cervical adenocarcinoma reveal a “cold” tumor-immune phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2375.