Endocrine Abstracts

Introduction: The association between medullary (MTC) and differentiated thyroid cancer (DTC, with the most frequent form of papillary thyroid carcinoma, PTC) is rare and can be observed in two main settings: a collision tumor (that is, a tumor with two separate and different components) or a mixed tumor showing dual differentiation.

Case report: A 58-year-old woman, affected by euthyroid multinodular goiter came to our observation for a second opinion regarding the surgical indications for their goiter. The thyroid antiperoxidase antibodies titer was elevated, ATPO: 40.7 UI/ml (normal values <5.61). An ultrasound scan revealed diffuse thyroid enlargement with a suspicious nodule (hypoechoic, with irregular margins, calcifications and intranodular hypervascularization) of 9.8/11.7 mm, recently described in the upper third of the left thyroid lobe. In both lobes, other micronodules hypo- or isoechoic were also described. The serum calcitonine (CT) was 78, repeated 82 pg/ml (normal values ≤ 2 pg/ml) and carcinoembrional antigen (CEA) was also elevated. The fine-needle aspiration cytology was nondiagnostic and patient was referred for surgery for total thyroidectomy with central compartment neck dissection. The histological examination confirmed the diagnosis of medullary thyroid cancer, showing a lymphocytic intratumoral infiltration and multiple occult follicular variant of papillary microcarcinoma in both lobes. One of this microcarcinoma was adjacent to the medullary carcinoma. No lymph node metastases were found. The serum levels of CT and CEA decreased to normal after the operation. Molecular analysis of the RET proto-oncogene was performed.

Conclusions: In our case, the simultaneous occurrence of MTC and multifocal PTC has the features of a collision tumor, although the close relationship of one of the foci of PTC with MTC has rise the hypothesis of a mixed tumor.