Abstract Background A large proportion of patients with foregut cancers do not receive guideline-concordant treatment (GCT). This study sought to understand underlying barriers to GCT through a root cause analysis approach. Methods A single-institution retrospective review of 498 patients with foregut (gastric, pancreatic, and hepatobiliary) adenocarcinoma from 2018 to 2022 was performed. Guideline-concordant treatment was defined based on National Comprehensive Cancer Network guidelines. The Ishikawa cause and effect model was used to establish main contributing factors to non-GCT. Results Overall, 34% did not receive GCT. Root causes of non-GCT included Patient, Physician, Institutional Environment and Broader System-related factors. In decreasing order of frequency, the following contributed to non-GCT: receipt of incomplete therapy ( N = 28, 16.5%), deconditioning on chemotherapy ( N = 26, 15.3%), delays in care because of patient resource constraints followed by loss to follow-up ( N = 19, 11.2%), physician factors ( N = 19, 11.2%), no documentation of treatment plan after referral to oncologic expertise ( N = 19, 11.2%), loss to follow-up before oncology referral ( N = 17, 10%), nonreferral to medical oncologic expertise ( N = 16, 9.4%), nonreferral to surgical oncology in patients with resectable disease ( N = 15, 8.8%), and complications preventing completion of treatment ( N = 11, 6.5%). Non-GCT often was a function of multiple intersecting patient, physician, and institutional factors. Conclusions A substantial percentage of patients with foregut cancer do not receive GCT. Solutions that may improve receipt of GCT include development of automated systems to improve patient follow-up; institutional prioritization of resources to enhance staffing; financial counseling and assistance programs; and development and integration of structured prehabilitation programs into cancer treatment pathways.