Simultaneous Medullary and Papillary Thyroid Cancer: A Novel Entity?

The causes underlying the phenomenon of simultaneous medullary (MTC) and papillary thyroid cancer (PTC) are unclear. This study of 26 patients with simultaneous MTC and PTC aimed at clarifying clinical and histopathologic characteristics and trends of this unusual condition among MTC and PTC patients who were operated on at a tertiary referral center in Germany. A total of 26 patients revealed simultaneous MTC and PTC, yielding the following rates: 2.6% (26 patients) among all 1019 PTC patients, 2.6% (6 patients) among all 235 hereditary MTC patients, 4.1% (20 patients) among all 492 sporadic MTC patients, and 3.6% (26 patients) among all 727 MTC patients. Simultaneous MTC and PTC were consistently smaller than nonsimultaneous MTC (6 vs. 13 mm for hereditary MTC, P = .16; 12 vs. 23 mm for sporadic MTC, P = .009; and 11 vs. 20 mm for any MTC, P = .008) and PTC (8 vs. 20 mm, P < .001). Simultaneous MTC and PTC increased among MTC and PTC patients over time: from 0% to 4.3% (PTC), from 0% to 4.6% (hereditary MTC), from 0% to 8.1% (sporadic MTC), and from 0% to 7.0% (any MTC). For sporadic MTC, these rates virtually doubled every 5 years. Of 6 patients with simultaneous hereditary MTC and PTC, 5 revealed late-onset REarranged during Transfection (RET) mutations (1 L790F carrier; 2 V804L and 2 S891A carriers). Greater pathologic scrutiny, in addition to environmental changes, explains the surge of simultaneous MTC and PTC in Germany. More data are needed from additional geographic areas and populations to delineate individual contributions of these factors.