Anaplastic Transformation of Papillary Thyroid Carcinoma in Metastatic Lymph Nodes

Author(s): Fukuda Yujiro, Fujita Naoaki, Hara Hitrotaka

Background: Anaplastic thyroid cancer (ATC) is a rare but highly aggressive malignancy, accounting for approximately 1–4% of all thyroid cancers and associated with extremely poor prognosis. Although anaplastic transformation most commonly arises within the primary thyroid tumor, transformation occurring in metastatic cervical lymph nodes is exceedingly uncommon. Early recognition of rapid clinical progression is essential, as timely diagnosis may influence management strategies. Case Presentation: We report the case of a 67-year-old woman who presented with a year-long right neck swelling and recent onset of hoarseness. Imaging revealed an enlarged right cervical lymph node with central necrosis and a 3-cm thyroid mass. Fine needle aspiration identified papillary thyroid carcinoma (PTC). The patient underwent total thyroidectomy with right modified radical neck dissection. Histopathology demonstrated conventional PTC in the primary lesion, whereas the metastatic cervical lymph node exhibited spindle cell proliferation with marked nuclear atypia, consistent with anaplastic thyroid cancer. Postoperatively, external radiation therapy was initiated; however, rapid disease progression ensued, with the development of cervical skin metastasis, lung metastases, and pleural involvement. The patient died 57 days after surgery despite treatment. Conclusion: This case highlights the rare occurrence of anaplastic transformation within metastatic cervical lymph nodes of PTC. Even with complete resection and postoperative radiation therapy, the disease course may be fulminant. Clinicians should remain vigilant for rapid morphological or clinical changes in metastatic lesions, as early detection of anaplastic transformation may improve diagnostic accuracy and inform treatment planning.