ESR1 and lung cancer: A hollow needle biopsy of the left breast and axillary lymph node was performed, which revealed invasive ductal carcinoma showing positivity for CK7, TTF-1, napsin-A (weak), E-Ca3, and 20% Ki-67 and negativity for estrogen receptor (ER), progesterone receptor (PR), c-erbB-2, P63, and GATA-3 (Fig. 4), confirming breast metastasis of lung cancer.