Cohexisting Medullary and Papillary Thyroid Cancer

Purpose: Papillary thyroid carcinomas (PTCs) and medullary thyroid carcinomas (MTCs) have always been considered different in terms of their incidence rates, cell origins, and histopathological features. Simultaneous occurrence of both disease entities is very rare. Methods: We describe a series of cases with simultaneous MTC and PTC occurrences in the thyroid gland. Results: From 2,897 patients (mean age, 49.2±12.5; 81% women) who underwent thyroidectomy for cancer between 2000 and 2015, we reviewed 11 cases of simultaneous occurrence of MTCs and PTCs. Multifocal PTC with simultaneous MTC was detected in 5 of the 11 cases (45%). Of these PTC patients, 2 had 2 foci, 2 had 3 foci, and 1 had 4 foci. There was 1 case of multifocal MTC with solitary PTC. One patient presented with “composite thyroid carcinoma” with mixed features of MTCs and PTCs. Eight patients (72%) presented an association with diffuse lymphocytic thyroiditis. The sizes of the tumors were 1.95±0.23 cm vs. 1.20±0.20 cm for PTCs and MTCs, respectively (P=0.531). The prevalence of extrathyroidal extension was 33.1% vs. 30.2% for PTCs and MTCs, respectively (P=0.282). All patients underwent total thyroidectomy and central neck node dissection. Radio iodine was delivered to 44% of patients. Follow-up review revealed 9 disease-free patients and 1 with local neck recurrence, while 1 patient died due to non-thyroid reasons. Conclusion: There are only 30 reports describing a total of 50 cases in the English literature regarding concurrent PTC and MTC in the same gland. This study represents one of the largest case series. Whether the incidence of another cancer in these patients is coincidental, or due to the possible activation of a common tumorigenic pathway for both follicular and parafollicular thyroid cells, remains to be elucidated.