Abstract Introduction: Certain retrospective and registry-based studies have indicated a higher risk of COVID-19 adverse outcomes in cancer, but a detailed understanding of the immune response in cancer patients and the impact of cancer therapy is needed. CAPTURE is a pan-cancer, prospective longitudinal study established in response to the unique challenges of SARS-CoV-2 pandemic for the care of cancer patients. Experimental Procedures: CAPTURE is a multicenter, UK-based longitudinal cohort study that commenced recruitment in May 2020. Study participants are recruited from a broad range of cancer types and cancer interventions and irrespective of their SARS-CoV-2 status, in order to capture both the nominator and the denominator. In addition to cancer patients, the study participants also include health care workers (HCW) for the purpose of studying transmission dynamics. Detailed clinical, epidemiologic, and demographic data are collected from all participants alongside a range of biologic samples that underpin case definitions and will facilitate immune monitoring. All participants will be followed up longitudinally for up to five years. Results: The overarching aim is to establish a prospective and unbiased understanding of the susceptibility and morbidity of COVID-19 in cancer patients and the patterns of viral nosocomial transmission. We will follow up patients long-term to understand the extent and duration of immunity and how immunity is impacted by cancer type, stage, and therapy. Our comprehensive sampling will help to draw a detailed picture of immune response to SARS-CoV-2 in cancer patients by monitoring active infection, antibody response, and T-cell activation, supplemented by detailed immunophenotyping, transcriptome, TCR/BCR sequencing, and germline profiling for HLA typing and identification of disease-associated polymorphisms. Finally, while there is a well-established correlation of circulating cytokine levels and Covid-19 severity, CAPTURE will identify early indicators of a maladapted inflammatory response in cancer patients by cytokine and chemokine profiling to establish early biomarkers of disease severity. Within the first month, we have recruited 95 participants (54% cancer patients, 46% HCWs) with matching swabs, plasma, PBMC, and whole blood for RNA sequencing. Two longitudinal samples were collected on average. Results from antigen and antibody profiling within this cohort will be presented at the meeting. Conclusion: CAPTURE will provide a detailed understanding of the interaction between immune response to SARS-CoV-2, cancer, and cancer treatments. Results will be informative in a wider health care context in order to minimize harm and maximize cancer outcomes in a sustainable manner. Furthermore, given inherent and iatrogenic defects in discreet immune cell subsets, this is a key patient cohort to inform a wider understanding of the immune response to SARS-CoV-2. Citation Format: Annika Fendler, Laurie Boos, Lewis Au, Scott Shepherd, Fiona Byrne, Kim Edmonds, Ellie Carlyle, Lyra Del Rosario, Ben Shum, James Larkin, Lisa Pickering, Andrew Furness, Samra Turajlic, on behalf of CAPTURE investigators. CAPTURE: Cancer and COVID-19 antiviral immune monitoring study [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2020 Jul 20-22. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(18_Suppl):Abstract nr PO-091.