Microscopically, both primary and metastatic tumors are characterized by proliferation of round to oval cells with histiocytoid cytoplasm showing signet-ring or vesicular features (10) as well as positivity for various apocrine or epithelial markers such as AE1/AE3, GCDFP 15, CK7, Ber-EP4, EMA, and CAM 5.2 and negativity for CK20, TTF1, and CDX2 (11). The gene discussed is TTF1; the disease is metastatic neoplasm.