Colonic metastasis from anaplastic thyroid carcinoma: The value of [18F]FDG PET/CT in an unusual presentation.

Anaplastic thyroid carcinoma (ATC) is an aggressive malignancy associated with poor survival and a metastatic pattern that typically involves the lungs. A patient with ATC harboring a papillary component and a BRAF V600E mutation, with locoregional invasion, was treated with surgery and radiotherapy following detection of residual disease. After a disease-free interval of 17 months, a lesion was identified at the splenic flexure of the colon, which was histologically confirmed as a metastasis from ATC. This case demonstrates an unusual metastatic site and emphasizes the value of [¹⁸F]FDG PET/CT in detecting atypical recurrences.