Squamous dedifferentiation and differentiated high-grade transformation of papillary thyroid carcinoma in metastatic lymph nodes: Two cases and literature review

Although it is extremely rare, papillary thyroid carcinoma (PTC) can exhibit unexpected behavior, with the potential to transform into more lethal forms in metastatic sites. This report describes 2 cases in which PTC transformed within metastatic lymph nodes. Case 1: A 57-year-old woman with a progressively enlarging right neck mass was found on imaging to have cervical lymphadenopathy and small right thyroid nodules. She underwent total thyroidectomy with neck dissection. Histopathology revealed metastatic PTC with squamous dedifferentiation in cervical nodes. Immunohistochemistry confirmed thyroid origin.

Case 2: A 45-year-old woman presented with right submandibular swelling. Ultrasound revealed a left thyroid nodule with suspicious cervical lymphadenopathy. She underwent total thyroidectomy with neck dissection. Histopathology showed conventional PTC with high-grade transformation in 1 metastatic lymph node, consistent with differentiated high-grade thyroid carcinoma. Seven cases of PTC transformation in metastatic sites were reviewed. Ages ranged from 56 to 79 years. Symptoms were neck masses, respiratory, and systemic symptoms. Most cases were conventional PTC. Transformation predominantly resulted in squamous cell carcinoma, though rarer transformations were present. The transformations were mainly regional, but distant metastatic sites such as the lung were also reported. Management included total thyroidectomy and neck dissections with radioactive iodine, often combined with chemoradiation or targeted therapy for advanced cases. Lymph node metastases originating from the thyroid may undergo histological transformation and exhibit aggressive behavior. Total thyroidectomy combined with radioiodine ablation and hormone therapy might yield favorable outcomes, but regional and distant metastases may still develop.