COLLISION TUMOR OF THE THYROID

A CASE OF MEDULLARY AND PAPILLARY THYROID CARCINOMAS WITH NODAL METASTASES

Abstract

INTRODUCTION
Papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) differ in their incidence, cell origin and histopathological features. Thyroid collision tumors have rarely been reported. We present a 69-year-old female who was recently diagnosed with a collision thyroid tumor consisting of PTC and MTC.

CASE
A 69-year-old female with underlying dyslipidemia presented with neck discomfort. On surveillance medical check-up, it was found that her carcinoembryonic antigen (CEA) was markedly elevated at 220.9 uG/L (<5). Computed tomography scan of thorax, abdomen and pelvis showed a suspicious left thyroid nodule and multiple enlarged lymph nodes at the left lower cervical and superior mediastinal. Subsequent fine needle aspiration (FNA) demonstrated medullary thyroid carcinoma. She underwent total thyroidectomy with modified radical neck dissection with sternotomy for removal of right paratracheal lymph nodes. Histopathology examination demonstrated medullary thyroid carcinoma measuring 35 mm with extensive perithyroidal soft tissue and lymph nodes infiltration. Seven out of twenty-two right lateral cervical lymph nodes, three out of four right paratracheal lymph nodes, and four out of thirteen left lateral lymph nodes were positive for metastases. Papillary microcarcinoma measuring 3 mm was also found at the right lobe. The calcitonin level was 2742 pg/ml postoperatively and decreased further to 1456 pg/ml six months later. CEA decreased to 45.4 uG/L. FDG-PET whole body scan reported no hypermetabolic lesions at the thyroid bed. Currently, she is on levothyroxine therapy (without TSH suppression) and on close follow-up.

CONCLUSION
The collision between two thyroid carcinomas is a rare entity. Management requires assessment of each carcinoma and tailored according to the extent of both tumors. In this case, the focus was on the predominant MTC.