Mixed medullary-follicular carcinoma is an uncommon tumor of the thyroid. It is characterized by histological and immunohistochemical features of both follicular and parafollicular C cells. We report two female patients, aged 26 and 78 years, with mixed medullary-follicular carcinoma. Histologically, the tumors are composed of follicular carcinoma areas and solid nests of polygonal cells consistent with medullary carcinoma. Immunohistochemically, thyroglobulin and calcitonin positivity was detected. Precise diagnosis of mixed medullary-follicular carcinoma is essential for accurate treatment and follow-up.

Mixed medullary-follicular carcinoma is an uncommon tumor of the thyroid. It is characterized by histological and immunohistochemical features of both follicular and parafollicular C cells. We report two female patients, aged 26 and 78 years, with mixed medullary-follicular carcinoma. Histologically, the tumors are composed of follicular carcinoma areas and solid nests of polygonal cells consistent with medullary carcinoma. Immunohistochemically, thyroglobulin and calcitonin positivity was detected. Precise diagnosis of mixed medullary-follicular carcinoma is essential for accurate treatment and follow-up.