NR4A1 and breast carcinoma: Studies of neoadjuvant chemotherapy or endocrine therapy in hormone receptor–positive (HR+) breast cancers have found pCR rates in the 1% to 17% range.7,8 As technology improves, stereotactic partial breast irradiation (sPBI) techniques and adaptive radiation give practitioners tools to immobilize the breast with geometric precision and sharper dose fall off,9,10 while safely delivering higher doses.11 Our previous phase 1 study using adjuvant sPBI, showed safety of up to 30 Gy in a single fraction.12 This was the basis of conducting an ablative trial with starting doses at 30 Gy.