Synchronous papillary thyroid carcinoma and medullary thyroid carcinoma - a pitfall waiting to happen.

Papillary thyroid carcinoma (PTC) is the most common thyroid carcinoma and is derived from thyroid follicular cells. In contrast, medullary thyroid carcinoma (MTC) is rare and originates from the parafollicular C-cells. Synchronous occurrence of these two carcinomas is uncommon and occurs as either discrete lesions or as a mixed lesion. The current case report describes a 50-year-old woman with synchronous multiple discrete MTC and PTC with lymph nodes metastasis. Pathologists and treating physicians should be aware of the synchronous coexistence of these entities to avoid possible misdiagnosis.