ODP469 Coexistence of two thyroid malignancies with Hurthle cell and Papillary thyroid carcinoma
Authors: Hamouche Walid , Gill Simrapreet , Faour Omar , Zahedi Tooraj , Zhang Fan 
Published: November 2022

Abstract

Background
The simultaneous presentation of mul tiple thyroid malignancies is a rare occurrence with each type of thyroid cancer having different cellular origins, histopathological appearance, and clinical course. Collision tumors representtwo histologically different tumor types occurring at the same anatomic region. When diagnosed within 6 months of the original they are also referred to as synchronous tumors. Papillary thyroid carcinoma (PTC) is the most common (80-85%) differentiated thyroid carcinomas (DTC), followed by follicular thyroid carcinoma (FTC) (10-15%), and Hurthle cell carcinoma (3–5%). We report a rare case of a patient with dual thyroid malignancy containing both PTC and Hurthle cell carcinoma in different thyroid lobes.

Case presentation
Patient is a 50 year old female with past medical history of hypertension and family history of thyroid disease in her sister and cousins, who presented with thyroid gland enlargement. Patient denied any hyper/hypothyroidism or compressive symptoms. Labs showed normal TSH and free T4. Thyroid ultrasound revealed a heterogeneous nodule with microcalcification in the right thyroid lobe and three well circumscribed left mid pole nodules. FNA thyroid biopsy of the right thyroid nodule demonstrated many Hurthle cells with uniform nuclei. The genomic classification identified multiple chromosomal copy number alterations consistent with a clonal neoplasm with intermediate-high risk for cancer, although no point mutations or gene fusions were found. Patient initially underwent right hemi-thyroidectomy and isthmectomy. Pathology confirmed two well circumscribed angioinvasive Hurthle cell carcinoma measuring 3.4×2.1×2. 0 cm and 1.6×1.5×1.4 cm with multiple foci of capsular invasion oncocytic features along with a 0.2 cm papillary thyroid microcarcinoma without extrathyroidal extension. After three weeks, patient proceeded with completion left thyroidectomy and showed a 1.2×1.1×1. 0 cm well circumscribed, partially encapsulated nodule, consistent with Papillary thyroid carcinoma (PTC). Lymph nodes were negative for metastasis. Patient received whole body I-131 scan and radioiodine ablation therapy. She was subsequently placed on Levothyroxine for thyroid hormone replacement and remained euthyroid without cancer recurrence.

Conclusion
Collision tumors account for 1% of thyroid malignancies with the most commonly reported combination being PTC and medullary thyroid carcinoma. Interestingly, this case presented with a rare finding of collision and synchronous tumors in the form of PTC and Hurthle cell carcinoma which was known to associate with increased chromosomal copy number instead of point genetic mutation. Previous literature have described collision effect, stem cell, hostage, and single progenitor theories in an attempt to explain the origin of these phenomena with possible molecular mechanisms. Clinicians should be aware that the dual thyroid malignancy with different histogenetic origin may co-exist in the same patient. The therapeutic strategy should be tailored based on each thyroid cancer variant with correlated biological behavior, clinical and genetic features.
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