Histopathology. a: Tumour with solid and invasive growth pattern surrounded by desmoplastic connective tissue (H&E, 40×). b: in detail: Hyperchromatic, pleomorphic nuclei with necrosis and numerous mitoses (H&E, 200×). c: Positive immunohistochemical staining for Cytokeratin 7 (CK7, 200×). d: Negativity for the thyroid transcription factor 1 (TTF-1, 200×).