Background: With recent Level I evidence (FAST FORWARD) supporting radiation therapy (RT) duration as short as one week and Level I evidence (CALGB9343) supporting RT omission in favor of antiestrogen endocrine therapy (ET) alone in select patients, the necessity of both RT and ET, adjuvantly, in early-stage breast cancer (BC) has been questioned. Evidence providing granular details on the role of insurance in the aggregate cost of RT and ET is lacking. This project disaggregates costs by insurance plan to increase transparency of out-of-pocket (OOP) cost estimates. Methods: National Comprehensive Cancer Network guidelines were utilized to determine the proper treatments, with FAST FORWARD radiation dose/fractionation (26 Gy in 5 fractions) representing RT. Treatments were identified using Current Procedural Terminology and Healthcare Common Procedure Coding System codes. OOP costs, deductibles, and copay/coinsurance were calculated for Medicaid, Original Medicare, Medigap Plan G, and Medicare Part D Rx. The medicare.gov, medicaid.oh.gov, aarpmedicareplans.com, and cms.gov were used to determine pricing. Price estimates reflect actual costs per insurance plan rather than costs estimated from claims data. All procedures were considered to be performed in an Ohio hospital setting, insurance coverages were based on the zip code 44106, and total expenses were based on all treatments plus a 5-year follow-up (not adjusted for inflation). Results: Treatment charges for ET include medical oncology initial consultation, biannual medical oncology follow-up, baseline bone density study, and Anastrozole cost (5-years). Treatment charges for RT include initial consultation, treatment planning, dosimetry calculations, treatment device, simulation and verification, RT delivery, on-treatment visits, and medical physics consultation. Original Medicare beneficiaries face an OOP cost of 20% for Medicare Part B claims with no cost cap for approved procedures after the deductible. Medications are covered under Medicare Part D with copays. This results in a marginal OOP treatment charge (after 5-year follow-up) of $767.54 for ET alone and $1,416.78 for ET + RT. Medigap Plan G beneficiaries face a marginal OOP charge of $1,225 for both ET alone and ET + RT, assuming the $226 Medicare Plan B deductible is met by the cost of lumpectomy during the year of RT. For Medicaid beneficiaries (assuming all treatments are approved by Medicaid), all expenses are covered without limit, resulting in no OOP expense for either treatment plan. Conclusions: Discussions of adding RT to ET for post-lumpectomy early-stage BC often involves considerations of treatment costs. This model (based on actual cost estimates per insurance plan rather than claims data) can help to enhance cost transparency by comparing expenses between Medicare and Medicaid plans.