Anaplastic transformation of metastatic papillary thyroid carcinoma lesion histologically mimicking a squamous cell carcinoma: A case report

Introduction: The incidence of anaplastic transformation of thyroid cancer from Papillary Thyroid Carcinoma (PTC) is a rare tumor event, which ranges from 1 to 2 % of all cases of thyroid malignancy. Anaplastic transformation is often reported in primary lesions, but is rarely found in metastatic lesions from Differentiated Thyroid Carcinoma (DTC). Presentation of case: This case report reports a unique tumor process where a 70-year-old woman had a metastatic lesion in the Mandible from PTC which transformed into ATC with histological features resembling squamous cell carcinoma-type. Immunohistochemical examination was able to prove that the lesion in the Mandible is a type of undifferentiated Thyroid carcinoma (anaplastic) with a squamous pattern originating from PTC. Discussion: This type of tumor with histological variant images that resemble other types of tumors is a challenge for diagnosis and appropriate management, so understanding the variants of this type of ATC is important for better management. Conclusion: Although rare, anaplastic transformation can occur in metastatic sites of PTC. This necessitates the need for early accurate diagnosis through IHC assessment and somatic mutation testing so that appropriate treatment can be delivered.