Out-of-pocket costs are burdensome for breast cancer patients. Cost-reducing interventions, though implemented, have unclear comparative efficacy. This study aimed to critically evaluate characteristics of successful versus unsuccessful interventions designed to decrease out-of-pocket costs for breast cancer patients. A systematic review was conducted in accordance with the PRISMA checklist. Embase, PubMed, Global Index Medicus, and Global Health were queried from inception to February 2021. Articles describing a financial intervention targeting costs for breast cancer screening, diagnosis, or treatment and addressing clinical or patient-level financial outcomes were included. Methodological quality was evaluated using the QualSyst tool. Interventions were organized in accordance with timing of implementation, with narrative description of intervention type, success, and outcomes. Of the 11,086 articles retrieved, 21 were included in this review. Of these, 14 consisted of interventions during screening, and seven during diagnosis or treatment. Free/subsidized screening mammography was the most common screening intervention; 91% of these programs documented successful outcomes. Patient navigation and gift voucher programs demonstrated mixed success. The most successful intervention implemented during diagnosis/treatment was reducing medication costs. Low-cost programs and direct patient financial assistance were also successful. Limitations included lack of standardization in outcome metrics across studies. Financial interventions reducing prices through free screening mammography and decreasing medication costs were most successful. Less successful interventions were not contextually tailored, including gift card incentivization and low-cost treatment modalities. These findings can facilitate implementation of broader, more generalizable programs to reduce costs and improve outcomes during evaluation and management of breast cancer.