<b>Case Presentation:</b> A 72-year-old woman with a history of Estrogen Receptor (ER)-positive (5%), Progesterone Receptor (PR)-negative, Human epidermal growth factor receptor-2 (HER2)-negative breast cancer (diagnosed 3 years prior) presented with right orbital pain, diplopia, and periorbital swelling. The gene discussed is ESR1; the disease is breast carcinoma.