Rare Mixed Thyroid Carcinomas: A Report of Two Cases

INTRODUCTION: Thyroid cancers constitute 0.5%- 1% of all cancers of which differentiated cancers are most common. Mixed thyroid carcinomas are rare entities comprising only 0.5% of thyroid cancers. These tumours pose challenges in diagnosis by fine needle aspiration cytology. CASE REPORT: Here, we present two rare cases of these mixed thyroid carcinomas. The first is that of a 21 year old female diagnosed with medullary thyroid carcinoma by the method of fine needle aspiration cytology (FNAC). She underwent definitive surgical treatment. Final histopathology revealed diagnosis of a nodular tumour with mixed features predominantly medullary carcinoma with areas of follicular carcinoma, confirmed on immunohistochemistry. Second report is that of a 45-year- old female diagnosed as medullary thyroid carcinoma on fine needle aspiration cytology (FNAC). Definitive surgical treatment was performed. Histopathology showed a mixed tumour with medullary and papillary components as confirmed through the process of immunohistochemistry. CONCLUSIONS: The knowledge of these rare carcinomas is important in avoiding a dilemma in management of this condition. Detection of these mixed tumours is difficult by FNAC. The definitive treatment essentially requires recognition of medullary component. We re-emphasize the importance of immune-histochemistry in arriving at an accurate diagnosis.