Endocrine Abstracts

Introduction: Papillary thyroid carcinoma (PTC) is the most common thyroid carcinoma and is derived from thyroid follicular cells which originate from the endodermal origin. In contrast, medullary thyroid carcinoma (MTC) is rare and originates from the parafollicular C-cells, which are commonly thought to be derived from the ectodermal neural crest. Co-incidence of the two condition on the same patient is so rare. We describe a case of concurrent MTC and PTC occurring in the same thyroid lobe.

Case report: A 63-year-old woman was referred to our hospital for further evaluation of thyroid nodules. Ultrasound assessment revealed two nodules in the right lobe, 10.3 mm and 14.4 mm in size with accompanying calcifications. Her serum levels of calcium, parathormone, carcinoembryonic antigen, thyroid stimulating hormone and free thyroxine were normal. The baseline serum calcitonin level was 139 pg/ml (normal range [NR] <11.5 pg/ml). There were no antithyroid autoantibodies. A single fine-needle aspiration biopsy (FNAB) was applied, the result was suspicious for malignancy. Abdominal US was negative for adrenal nodules as well as urinary catecholamines and metanephrine levels were within normal limits. Total thyroidectomy was performed. The pathological examination revealed the presence of a tall cell type papillary carcinoma of the right lobe (1.5 cm) with an adjacent medullary microcarcinoma (0.6 cm). The tumour cells were positive for calcitonin. The postoperative TSH level was 40 mIU/ml (NR 0.3–4.9) and calcitonin level was <2 pg/ml. The patient was discharged without any complications. An ablative dose of iodine 131 treatment is planned.

Discussion: The synchronous occurrence of multiple thyroid carcinomas of different origin in the same patient is extremely rare, representing less than 1% of all thyroid malignancies. Interestingly, the incidence of PTC in patients with MTC is greater than that of PTC in patients undergoing thyroidectomy for non-malignant conditions, suggesting the presence of a common pathogenic etiologies. Even if it can be coincidental, possible hypotheses for the synchronous occurrence include involvement of the RET proto-oncogene in both PTC and MTC and an unidentified common mother cell with a capacity for differentiating parafollicular C cells and epithelial follicular cells which can be the origin of the cancer. Beacuse there is a lack of marked differences in the ultrasonografic features between MCT and PTC, the possibility of the coexistence must be taken into account. Since there is no evidence of a certain cause of this condition more data is needed from additional geographic areas and populations.