Mixed medullary and follicular or papillary carcinoma of thyroid is an extremely rare tumor, characterized by coexistence of morphological and immunohistochemical features of both medullary carcinoma and follicular (or papillary) carcinoma. This case report describes for the first time in the indexed database a late recurrence of a medullary thyroid carcinoma initially diagnosed as follicular-papillary form, treated and monitored accordingly. After 14 years, a superior mediastinum tumor was discovered incidentally at a thorax computer tomography. The whole-body I-131 scan was negative and F-18 FDG-PET-CT showed glucose avidity of the tumor. The patient was operated on and the histology revealed medullary thyroid carcinoma. If there are no possibilities to have routinely extensive immunohistologic profiles, it is recommended to check the serum calcitonin, at least in any patient with confirmed thyroid carcinoma. 1. Introduction Thyroid carcinoma is the most frequent endocrine cancer, accounting for about 5% of thyroid nodules  with a general incidence reported to be between 1.2 and 3.8 100.000 inhabitants [2, 3]. The differentiated thyroid cancers represent about 80% of all thyroid cancers , with a good prognosis [4, 5], while medullary, respectively, anaplastic forms, with considerable lower incidences [1, 6–9], have an aggressive evolution, frequently very severe and fast. The mixed forms are very rare and considered to be of different cell origins, with specific clinical behaviours [10–15]. Considered rare among human malignancies, the thyroid carcinoma has a very important increasing incidence in the last 10 years [3, 16], reported by studies from all over the world, with the fact that requires a new approach regarding the management of this pathology and special attention to the unusual or more aggressive forms. 2. Case Presentation A 67-year-old male was admitted to our institute with the diagnostic of multiple cervical lymph nodes and right thyroid nodule. He was submitted to total thyroidectomy, with selective right lymphadenectomy for a follicular-papillary thyroid carcinoma with right cervical lymph nodes metastasis, T3N1？M0, stage III, according to the TNM of the moment . At 4 weeks after the surgery, without thyroid hormone replacement the patient was evaluated prior to the metabolic irradiation with I-131. Therefore, the serum level of the thyroid-stimulating hormone (TSH) was >100？mIU/L, increased; the thyroglobulin (Tg) specific tumor marker was 13.2？ng/mL (N.V. < 0.1？ng/mL, undetectable in case of cured patients); the
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