Simultaneous occurrence of medullary and differentiated thyroid carcinomas. Report of 4 cases and brief review of the literature.

: Simultaneous occurrence of medullary thyroid carcinoma (MTC) and papillary thyroid carcinoma (PTC) in a single patient is an unusual event. The incidence, cell origin, histopathology features and prognosis of these two carcinomas are considered completely different. The aim of this retrospective study was to describe clinical, pathologic characteristics and the prevalence of diagnosing such patients in our clinic. Between October 2003 and December 2013, 1.420 consecutive patients diagnosed by histology as having differentiated thyroid carcinoma (DTC) and treated with radioactive iodide (RAI) were retrospectively investigated. Of these, 4 patients were diagnosed by histology as having simultaneous MTC and PTC. The clinical and pathology characteristics of these patients are described. The prevalence of simultaneous MTC and PTC of these 4 patients in our clinic was 0.28% of all patients with DTC. The age of the 4 patients ranged from 44 to 63 years and were three females and one male. These patients are currently alive without disease from either of the two types of cancer. In two of these patients, MTC was located in the left and PTC in the right thyroid lobe. One patient had MTC in the right lobe and PTC in both lobes. The remaining patient had both cancers in the left lobe as a mixed tumor. We are able to present the pathology of only 2 of these 4 patients. In these 2 patients MTC was located in the left and PTC in the right thyroid lobe, one of them was female and the other was male, aged 44 and 49, respectively. In conclusion, our results suggested that simultaneous occurrence of MTC and PTC had a prevalence in our clinic of 0.28% among 1420 consecutive patients with DTC or 0.14%, if only the 2 patients in whom we are able to present their pathology slides are considered. Our cases suggest that these two tumors are usually independent and coincidental events in every patient.