INTRODUCTION: Guidelines allow for the omission of sentinel lymph node biopsy (SLNB) and post-lumpectomy radiotherapy in women ≥ 70 years of age with hormone receptor-positive (HR +) breast cancer. Despite this, national data suggest these procedures have not been widely de-implemented. OBJECTIVES: Our objectives were to evaluate trends in SLNB and post-lumpectomy radiotherapy utilization in patients who are eligible for omission, and evaluate patient preferences as a target for de-implementation of low-value care. METHODS: We performed a sequential explanatory mixed-methods study by first analyzing an institutional database of patients ≥ 70 years of age with HR + breast cancer who received surgical treatment from 2014 to 2018. Based on the quantitative data, we conducted semi-structured interviews with women identified as high or low utilizers of breast cancer treatments to elicit patient perspectives on de-implementation. RESULTS: SLNB and post-lumpectomy radiotherapy were performed in 68% and 43% of patients, respectively, who met the criteria for omission. There was a significant decrease in SLNB rates from 2014 to 2018. Forty-nine percent of patients were classified as high utilizers and 26% were classified as low utilizers. Qualitative analysis found that the most important factors influencing decision making regarding SLNB and post-lumpectomy radiotherapy omission for both high and low utilizers were trust in their provider and a desire for peace of mind. CONCLUSIONS: Despite efforts to de-implement low-value care, older women with HR + breast cancer remain at risk of overtreatment. Patient perspectives suggest that multi-level de-implementation strategies will need to target provider practice patterns and patient-provider communication to promote high-quality decision making and reduction in breast cancer overtreatment.