Even when guidelines recommend multidisciplinary care, it is often unclear who should be accountable for that care.19 For example, if a patient with early-stage estrogen receptor–positive breast cancer does not receive endocrine therapy after lumpectomy and radiation, it may be unclear whether the lack of treatment should be attributed to the patient’s surgeon, radiation oncologist, and/or medical oncologist. This evidence concerns the gene ESR1 and breast carcinoma.