Purpose: Standardized treatment protocols for Wilms tumor have been developed for use in low- and middle-income countries (LMICs), but equivalent outcomes as high-income countries are not achieved outside of clinical trials. To identify critical breakpoints in protocol adherence contributing to reduced outcomes, we evaluated treatment compliance and impact of the completion of each stage of therapy on outcomes for Wilms tumor patients at a regional cancer referral hospital in northern Tanzania. Methods: This is a retrospective single-center cohort study for children diagnosed with Wilms tumor from 2016-2019 in Tanzania, treated per the International Society of Pediatric Oncology (SIOP) Africa adapted (2016-17) or standard (2018-19) therapy protocols. Treatment compliance was evaluated for both timing of chemotherapy initiation, and completion of risk-adapted therapy duration per protocol. Results: A total of 72 patients were evaluated. The two-year overall survival and event-free survival rates were 44% and 27%, respectively. Only 22% of patients completed recommended chemotherapy per protocol. There were delays at each stage of treatment, especially time to surgery (74 days), pathology report (32 days), and initiation of postoperative chemotherapy (39 days). A total of 38% of patients abandoned care, with 44% of abandonment occurring prior to surgery, 30% immediately after surgery, and 26% during post-operative chemotherapy. Compliance with surgical resection (p=0.05) and postoperative chemotherapy (p=0.04) were predictive of two-year overall survival. Conclusion: Standardized Wilms tumor treatment protocol compliance outside of clinical trials is low in many LMICs. In the current study, noncompliance with recommended chemotherapy correlated to reduced overall survival rates, with several identified key health system delays contributing to poor compliance. Future interventions targeting health system delays are critical to improve protocol compliance, increasing overall survival for pediatric Wilms tumor patients in LMICs. Citation Format: Austin Wesevich, Mocha George, Frank Kiwara, Colin Chao, Idd Shabani, John Igenge, Kristin Schroeder. Breakpoints in Protocol Compliance and Their Influence on Outcomes for Children with Wilms Tumor in Northern Tanzania [abstract]. In: Proceedings of the 9th Annual Symposium on Global Cancer Research; Global Cancer Research and Control: Looking Back and Charting a Path Forward; 2021 Mar 10-11. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2021;30(7 Suppl):Abstract nr 102.