Synchronous Presence of Papillary, Medullary, and Anaplastic Thyroid Tumors in a Single Patient: A Rare Case Report.

BACKGROUND Papillary thyroid carcinoma (PTC) is the most common form of thyroid cancer, while medullary thyroid carcinoma (MTC) and anaplastic thyroid carcinoma (ATC) are far less common. ATC is the most aggressive form, contributing to the majority of thyroid cancer-related deaths. While the coexistence of different pathological types of thyroid malignancies has been reported, including combinations of ATC, PTC, and poorly differentiated thyroid carcinoma, the detection of ATC within extrathyroidal metastatic lymph nodes remains exceedingly rare and of notable clinical significance. CASE REPORT We present a 68-year-old woman evaluated for a progressively enlarging right-sided neck mass which was apparat in clinical examination, with no other associated symptoms or signs. Nasopharyngoscopy was unremarkable. Imaging studies revealed a large cystic and necrotic mass in the right carotid space compressing the internal jugular vein. A core needle biopsy confirmed metastatic PTC. The patient underwent total thyroidectomy with right radical neck dissection. Histopathological evaluation reported a unique combination: a collision tumor composed of PTC, infiltrative follicular subtype, and MTC. Immunohistochemistry confirmed the diagnoses, and molecular analysis revealed a BRAF mutation. The patient was not a candidate for radioactive iodine therapy due to the aggressive nature of the anaplastic component. Thus, she was referred for targeted cancer therapy. CONCLUSIONS This case highlights the synchronous occurrence of PTC, MTC, and ATC in a single patient. The localization of anaplastic transformation solely to lymph nodes without thyroidal involvement underscores the importance of meticulous histopathological assessment. Comprehensive diagnostic workup and molecular profiling are critical in guiding treatment for such complex presentations.