OBJECTIVES: Financial access to medical technologies in the United States may be driven by many factors, including drug costs, health insurance coverage, benefit designs, and patients’ ability or willingness to pay for treatment. Studies evaluating out-of-pocket costs for cancer treatment have been conducted; however, no national models of financial access currently exist.METHODS: We developed a conceptual framework for an interactive model of financial access to cancer therapy. To illustrate the model's operation, we applied it to treatment of HER2+ breast cancer patients. The model traces the flow of patients along pathways of a decision tree. Beginning with the US population, the model branches by sex, breast cancer or no breast cancer, HER2+ or HER2- cancer, and insurance status. Only patients in the HER2+ branch are followed forward through the model. Patients are stratified by payor and benefit design, eligibility for patient assistance programs, and ability to pay for treatment without spending more than a pre-specified percentage of family income out-of-pocket. Data sources include custom analyses of publicly available databases (to determine incidence/prevalence and the annual income and expenditures of breast cancer patients), clinical trial data on dosages, and national survey data on the proportion of patients with different benefit designs. The user interface allows for unlimited variations in key input parameters.RESULTS: Model outputs include a series of graphs showing financial access before and after adding specific treatments, with and without support from patient assistance programs. Results are presented by payor, age, and income. Sensitivity analyses can be conducted to evaluate the robustness of results.CONCLUSIONS: While it is difficult to ascertain the number of patients who are not receiving treatment because of financial barriers, it is possible to develop a model that appropriately considers the main drivers of financial access to estimate the impact of financial barriers.