Endocrine Abstracts

Mixed medullary-follicular carcinomas (MMFC) of the thyroid are rare tumors which represents <0.15% of all thyroid tumors showing the morphological and immunochemical properties of both parafollicular and follicular cell lineages. Cases were immunoreactive for both calcitonin and thyroglobulin.

Case 1: A 25-year-old female patient referred us for evaluation of a thyroid mass located on the left lobe. Ultrasonography (US) revealed 38 mm solid isoechoic nodule with well-defined margins on the left lobe. An US-guided fine needle aspiration (FNA) was performed and reported as follicular neoplasm. A total thyroidectomy with central lymph node dissection was performed. Immunostaining revealed that the tumor cells were diffusely positive for calcitonin and chromogranin. Further, there were scattered follicles that stained positively with antibody against thyroglobulin. The histological findings in correlation with the immuneprofile, support a diagnosis of MMFC. Post-operatively calcitonin level was 2.69 pg/ml. Radioactive iodine ablation with 150 mCi and L-thyroxine supression theraphy had given to the patient.

Case 2: A 46-year-old female patient admitted with enlargement of a neck mass. US revealed 33 mm solid isoechoic nodule with ill-defined margins and microcalcifications on the left lobe of thyroid. US-guided FNA was reported as thyroid neoplasm with differentiation or anaplastic transformation. Patient’s serum level of calcitonin was 1802 pg/ml (normal <12 pg/ml). Results of blood testing for pheochromocytoma and hyperparathyroidism were within the normal range. Total thyroidectomy with central lymph node dissection was performed. The histological findings were consistent with MMFC with metastatic lymph nodes. The serum calcitonin level dropped to 3.75 pg/ml following the surgery.

Conclusion: The majority of MMFC occurs in a sporadic form, rarely it can be a component of MEN type 2. MMFC, medullary and follicular thyroid cancer behave differently in terms of clinical course and management. Identification of MMFC by FNA may be difficult, the proper immunostaining panel could have showed the different aspects of the mixed tumor.