A 39-year-old male with stage IIB (cT2N1M0) estrogen receptor (ER)–, progesterone receptor (PR)–, and human epidermal growth factor receptor 2 (HER2)–positive invasive ductal adenocarcinoma of the left breast presented with fatigue, fever, chills, nonproductive cough, and exertional shortness of breath. The gene discussed is ESR1; the disease is invasive ductal breast carcinoma.