Anaplastic Transformation of Papillary Thyroid Carcinoma Only Seen in Pleural Metastasis: A Case Report with Review of the Literature

Anaplastic transformation of papillary thyroid carcinoma (PTC) at distant metastatic sites is extremely rare, and there have been fewer than 20 reported cases in the literature. A 61-year-old woman presented with 1-week history of dyspnea. Her past medical history was remarkable because, 19 years ago, she underwent nearly total thyroidectomy and radical neck dissection due to PTC. Computed tomography of the chest revealed a 1.7 cm nodule in the lung and diffuse pleural thickening. Gun biopsy of the lung nodule revealed metastatic PTC with typical histology. However, the pleural biopsy predominantly showed anaplastic pleomorphic and spindle sarcomatoid carcinoma with microscopic focus of PTC. Immunohistochemical results showed both anaplastic sarcomatoid and PTC components positive for TTF-1, galectin-3 and PAX-8, thus supporting anaplastic transformation of PTC at the metastatic site. Subsequently the patient received 1 cycle of cisplatin-based chemotherapy but died from the disease 4 months after diagnosis. Although it is rare, anaplastic transformation of PTC should be considered during differential diagnosis of patients who present with exclusive sarcomatoid morphology at metastatic sites and have a history of PTC. We report another case of anaplastic transformation of PTC, found at pleural metastasis, together with the immunohistochemical profile and a literature review.