Simultaneous medullary and papillary thyroid cancer: two case reports.

BACKGROUND: Papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) have always been considered different from each other; in their incidence, their cell origin and their histopathological features. CASE PRESENTATION: This paper describes two rare cases of the simultaneous occurrence of MTC and PTC in the thyroid gland. Case 1 is unique for different reasons: (a) the patient was affected by both multicentric MTC and PTC; (b) a "composite thyroid carcinoma" with mixed feautures of MTC and PTC carcinomas was found in the istmus of the gland; and (c) these tumors were associated with diffuse lymphocytic-type thyroiditis (LT). Case 2 is notable for the long follow up: 16 years disease free. CONCLUSION: There are only 16 reports in the English medical literature describing a total of 20 cases of concurrent occurrence of both PTC and MTC in the same thyroid gland. We discuss whether the finding of another cancer in these patients was coincidental or from possible activation of a common tumorigenic pathway for both follicular and parafollicular thyroid cells.