Anaplastic thyroid carcinoma mimicking a malignant pleural mesothelioma: Clues for diagnosis.

Pleural metastasis of thyroid carcinoma is very rarely encountered in the evaluation of pleural effusion and diagnosis may be challenging. However, an anaplastic transformation of papillary thyroid carcinoma (PTC), although a rare condition, should be considered even after a prolonged period of patient follow-up. Here we report a case of anaplastic thyroid carcinoma mimicking malignant pleural mesothelioma diagnosed nine years after the initial diagnosis of PTC and detail the clues used to orient and confirm the diagnosis.