ABSTRACT
The medullary thyroid carcinomas (MTC) comprise 5-10% of all thyroid carcinomas. It is known to show many cyto-architectural variations. The WHO classification of thyroid tumors includes an entity called mixed medullary-papillary carcinoma, a rare malignancy known to represent <1% of all thyroid malignancies. Fewer than 40 such cases have been reported so far and include tumors showing morphological features of both medullary carcinoma and papillary carcinoma with immunoreactivity for calcitonin and CK19 &thyroglobulin respectively. We report a case of a 27-year-old female with complaints of gradually increasing neck swelling for 2 years, with difficulty in swallowing in the last 2 months. The swelling was more localized towards left. Ultrasound neck revealed a nodule in the left lobe of thyroid with benign features most likely nodular colloid goiter. Thyroid profile of the patient was normal. FNA revealed sheets and follicles lined by both hyperplastic and involutional follicular cells. Few micro follicles showed pleomorphic cells having hyperchromatic nuclei and mild anisonucleosis. A diagnosis of colloid goiter was given on cytology; however, on grounds of suspicion of a neoplastic process, histopathology was advised. The patient underwent total thyroidectomy. Hematoxylin & Eosin stained sections showed features of mixed medullary-papillary carcinoma of the thyroid which was further confirmed on Immunohistochemistry and raised serum calcitonin levels. It is important to know about this entity due to its prognostic implications, association with other endocrine disorders and to prevent any diagnostic dilemmas.