P-68 Misdiagnosed calcitonin negative Medullary thyroid carcinoma as Hurthle cell thyroid adenoma with fine needle aspiration biopsy

Abstract

Abstract Introduction Medullary carcinoma is a rare thyroid carcinoma, that originates from the malignant proliferation of parafollicular C cells. Medullary thyroid cancer produces calcitonin, and elevated calcitonin level is an essential feature of this tumor, so, most of them are associated with high levels of calcitonin. Calcitonin-negative medullary carcinoma of the thyroid gland is an extremely rare entity and poorly understood primary neuroendocrine carcinoma that is characterized by classic medullary carcinoma of the thyroid morphology without raised serum calcitonin levels. Fine needle biopsy (FNAB) is a diagnostic test done in people with suspected thyroid cancer and it is very important for timely diagnosis and treatment of medullar thyroid cancer, especially when calcitonin levels are in normal range. Clinical Case A 35-year-old woman visited an endocrinologist due to swelling on the left side of the neck. Thyroid ultrasound showed hypoechogenic, heterogenous nodule in the left lobe with dimensions 29×28×35 mm and calcifications. Laboratory tests were normal: thyroid stimulating hormone (TSH) 3,0 mlU/ml; free T4 14,3 pmol/l; anti –thyroid peroxidase antibody (ATPO) 20IU/ml; human thyroglobulin 35IU/ml; calcitonin <2 pg/ml; carcinoembryonic acid (CEA) 0.742ng/ml. The FNAB were performed, with cytological finding for classification group I. Four months after the first biopsy, the FNAB was repeated and Hürthle cells were found, with pronounced degenerative changes as well as pronounced cytological atypia, cytological findings correspond to classification group III. Computed tomography of the neck was performed preoperatively and it showed hypodense nodule (slightly smaller than 4 cm) with numerous calcifications, and no significantly enlarged lymph nodes. Left lobectomy was performed with histopathological findings for Medullary thyroid carcinoma. Immunohistochemical tumor cells were positive for chromogranin A, CD56, focally for thyroglobulin and CK 19, and negative for S-100 and NSE. RET gene mutation analysis was performed and it was negative. Additional diagnostic tests were performed for MEN2A and MEN 2B and they were excluded. Postoperative levels of calcitonin and CEA were in normal range. Conclusion Normal calcitonin levels do not exclude medullar carcinoma. Follow-up and monitoring of the patients with thyroid nodules is very important for timely diagnososis and treatment of medullar carcinoma.