Endocrine Abstracts

Introduction: Papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) are distinct neoplasms, associated with different histological findings. Their coexistence in the same patient is a rare event, requiring a different clinical approach.

Clinical case: A 72-year-old patient with no family history of thyroid disease, underwent total thyroidectomy in February 2019, due to toxic multinodular goitre, with no evidence of postoperative complications. The anatomopathological study of the surgical specimen revealed aspects of follicular nodular hyperplasia, with a 6 mm papillary microcarcinoma evident in the right lobe, with areas of classical pattern and a 4 mm medullary microcarcinoma in the left lobe (positive immunohistochemistry for calcitonin). Both lesions did not present foci of lymphovascular permeation or extension to the surrounding soft tissues. Two months postoperatively, patient was revaluated under 125 µg sodium levothyroxine id and presented: TSH 3.13 µUI/ml (0.38–1.33), fT4 12.8 pmol/l (7.9–14.4), Tg 0.31 ng/ml (1.15- 130.77), Anti-Tg Ab 8.7 IU/ml (5.0–100.0), Calcitonin 1.9 ng/l (<9.8) and CEA 1.9 ng/ml (<3.0). At this stage, a therapeutic change was made to 137 µg id levothyroxine sodium. In the cervical ultrasound study, a small amount of tissue, compatible with thyroid residue, was evident in the left locus. At 6 months postoperatively, the patient was revaluated again, showing clinical stability, with analytical study revealing: TSH 1.58 µUI/ml, fT4 14.2 pmol/l, Tg 0.24 ng/ml, Anti-Tg Ab 8.7 IU/ml, Calcitonin 1.8 ng/l (<9.8), CEA 2.0 ng/ml (<3.0), PTH 50.6 pg/ml (12.0–88.0) and assays of urinary catecholamines and metanephrines within the reference limits. The ultrasound study revealed at this stage that residual tissue remained in the left surgical bed, with maintained dimensions. Given the stability, patient continued therapy with 137 mg sodium levothyroxine, with indication for clinical, analytical and ultrasound reassessment in consultation.

Conclusions: The simultaneous occurrence of PTC and MTC is an unusual finding. The follow-up should consider the individual characteristics of both, as they consist in entities with different histological patterns and different clinical evolution. The aetiology of this entity is not clear, however, the possibility of a common tumour pathway should be placed and evaluated in series with a higher number of patients.