Endocrine Abstracts

Carcinoma showing thymus-like differentiation (CASTLE) is a rare malignancy, localized in the thyroid parenchyma. As far as we know, only a few CASTLE cases are described in literature. The diagnosis is based on immunoreactivity, the main characteristic is positivity to CD5, which reveals a thymic differentiation. We report the case of a 63-years-old male, who presented with a 3 cm solid, hypoechoic nodule in the lower part of the left thyroid lobe, with underlying structures fixation. The ipsilateral lymph node involvement was noted. The mass was irregularly shaped and adherent to the tracheoesophageal area, with a mass effect on the trachea, in his cervical superior mediastinal portion. Vessel displacement was recorded, as the tumor was in contact with the left common carotid artery in posterior, with jugular vein in posterolateral, and right common carotid artery inferior. He was surgically treated by a subtotal thyroidectomy with central neck dissection. The histopathologically and immunohistochemically exam revealed carcinoma, showing thymus-like differentiation (CASTLE) with cluster of differentiation 5 (CD5) (+), tumor protein p63 (p63) (+). Postsurgical chemotheraphy was applied (6 cycles with carboplatin and paclitaxel), afterwards external beam radiation (66 Gy/33 fractions/50 days). The diagnosis of CASTLE is a challenge for the physician, as there is a great resemblance with anaplastic thyroid carcinoma and squamous-cell carcinoma of the thyroid. A correct diagnosis is essential because the treatment and prognosis is different. CASTLE is an indolent and slow-growing malignancy, with a great response to chemo and radio therapy. In our case, extrathyroidal infiltrations and nodal metastasis are risk factors that are seriously decreasing the patient life expectancy.