© 2017 American Cancer Society BACKGROUND: There is increasing evidence that radiation therapy (RT) can be omitted for select older patients who are compliant with hormonal blockade, but there is no recent claim-based analysis for determining patterns of care and guiding possible treatment recommendations. METHODS: Medicare beneficiaries who were 65 years old or older and were diagnosed with breast cancer at 1 of 12 cancer centers affiliated with an academic center in the southeastern United States were analyzed. Stage 0 or I patients treated with lumpectomy from 2012 to 2014 were identified. Patient, treatment, and center characteristics were analyzed for the utilization of RT. RESULTS: Among 800 women treated with lumpectomy, 64% received adjuvant radiation. The median age was 74 years. The omission of RT was more likely in older patients, stage 0 patients, and patients with more comorbidities (P <.01). Hormonal blockade was used in 41% of the patients who did not receive RT. The utilization of hormonal blockade with the omission of RT was more likely in patients with fewer comorbidities (P <.01). CONCLUSIONS: In an older cohort of patients who otherwise would have qualified for the omission of radiation, two-thirds were treated with radiation. Future guideline recommendations should address omission in the context of hormonal blockade compliance because only 41% of the patients used hormonal blockade when radiation was not delivered. Cancer 2018;124:475-81. © 2017 American Cancer Society.