We report a rare case of mixed medullary-follicular carcinoma and papillary
carcinoma of the same thyroid. A 27-year-old Chinese female complained of
a single thyroid nodule for 2-3 months. Needle aspiration revealed suspicio
us papillary carcinoma and thyroidectomy performed later showed mixed medul
lary-follicular carcinoma and papillary carcinoma of the same thyroid which
was extremely rare. Whether neoplastic transformation is due to tumorigeni
c stimulus or just due to the collision phenomenon is still controversial f
or its etiology.